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PLANT    LIFE 

CONSIDERED   WITH   SPECIAL   REFERENCE   TO 
FORM   AND   FUNCTION 


BY 

CHARLES   REID   BARNES 

Professor  of  Plant  Physiology  in  the   University  of  Chicago 


NEW    YORK 

HENRY  HOLT  &  COMPANY 
1898 


Copyright,  1898, 

BY 

HENRY   HOLT  &  CO. 


ROUBHT    DKUHHiiNI)      I'KINTHR,     NKV 


PREFACE. 

In  recognition  of  the  fact  that  the  study  of  botany  in  the 
past  has  been  too  much  a  study  of  books  about  plants,  numer- 
ous laboratory  manuals  have  been  published  which  make  pos- 
sible the  study  of  plants  themselves.  Laboratory  work  has 
now  become  well-nigh  universal.  With  the  strenuous  insist- 
ence that  this  method  should  be  used  in  the  secondary  schools, 
there  has  been  a  growing  danger  that  such  study  would  de- 
generate into  mere  memory  training,  unless  the  relation  of 
the  facts,  often  entirely  isolated  in  the  pupil's  mind,  were 
clearly  brought  out.  Since  laboratory  study  soon  came  to 
include  the  examination  of  the  lower  plants  as  well  as  seed 
plants,  and  has  now  begun  to  include  some  experiments  in 
their  physiology,  the  absence  of  an  elementary  account  of 
the  form  and  functions  of  plants  of  all  groups  has  made  itself 
felt.  I  am  not  aware  that  any  book  at  present  attempts  to 
meet  this  need. 

To  the  proper  teaching  of  botany  in  secondary  schools 
such  a  book  is  indispensable.  However  capable  the  teacher 
may  be  to  gather  up  the  facts  observed  in  the  laboratory  and 
to  relate  them  with  others  so  as  to  produce  a  clear  concep- 
tion of  plant  life,  he  cannot  wisely  rely  upon  the  lecture  for 
pupils  of  13  to  18  years.  They  need  the  printed  page, 
which  appeals  to  eye  as  well  as  ear,  if  the  principles  and  facts 
are  to  be  firmly  grasped. 

iii 


IV  PREFA  CE. 

Plant  Life  is  an  attempt  to  exhibit  the  variety  and  pro- 
gressive complexity  of  the  vegetative  body;  to  discuss  the 
more  important  functions;  to  explain  the  unity  of  plan  in 
both  the  structure  and  action  of  the  reproductive  organs  ; 
and  finally  to  give  an  outline  of  the  more  striking  ways  in 
which  plants  adapt  themselves  to  the  world  about  them.  I 
have  made  an  effort  to  treat  these  subjects  so  that,  however 
much  the  student  may  have  still  to  learn,  he  will  have  little 
to  unlearn  ;  for  eradication  of  false  notions  is  the  despair  of 
the  college  teacher  of  science. 

This  is  not  a  book  to  be  memorized  and  recited.  If  so  used  it 
is  abused.  It  aims  to  be  intelligible  to  pupils  13  to  18  years 
of  age  who  are  engaged  in  genuine  laboratory  study — not  at 
irregular  hours,  without  supervision,  in  a  school  desk,  or  at 
home,  but  in  a  suitable  laboratory,  with  regular  time  (an 
hour  and  a  half  daily  if  possible),  under  the  direction  of  a 
live  teacher  who  has  studied  far  more  botany  than  he  is 
trying  to  teach.  I  am  aware  that  such  conditions  are  yet 
unrealized  in  many  schools ;  but  they  may  be  gradually 
reached.  That  Plant  Life  may  prove  useful  in  botanical 
instruction  even  under  the  most  unfavorable  conditions,  I 
permit  myself  to  hope  rather  than  to  expect. 

This  book  may  be  used  to  supplement  any  laboratory  guide 
or  the  directions  prepared  by  the  teacher.  For  the  sake  of 
teachers  who  may  not  wish  to  use  two  books,  or  who  lack  time 
and  facilities  for  preparing  laboratory  directions,  I  have  out- 
lined a  course  of  study  in  Appendix  I  which  can  be  carried 
out  with  the  equipment  listed  in  Appendix  III.  A  description 
of  the  material  needed  and  of  suitable  methods  of  preserving 
it  forms  Appendix  II.  Each'teacher  will,  of  course,  need  to 
modify  the  directions  to  suit  the  material  available.  I  have 
always  found  it  easier  to  prepare  directions  to  fit  the  material 
than  to  create  the  material  to  fit  the  directions.  The  "dem- 
onstrations "  of  Appendix  I  air  intended  as  suggestions  to  the 


rREFA  CE.  V 

teacher  of  things  which  it  is  advisable  to  show  to  pupils  under 
the  compound  microscope,  in  case  inadequate  equipment, 
lack  of  time,  or  difficulty  of  preparation  forbid  class  study. 

I  have  made  the  directions  fullest  in  relation  to  cryptogams 
and  physiology  because  these  fields  are  most  unfamiliar  to 
teachers  at  present.  Further  directions  for  the  study  of  seed 
plants  can  readily  be  provided  from  the  books  listed  in  Ap- 
pendix IV. 

For  laboratory  study  it  is  necessary  to  select  certain  illus- 
trative types  and  observe  their  structure.  In  the  text  I  have 
not  specifically  discussed  these  plants,  but  have  treated  gen- 
eral topics  so  as  to  correlate  the  facts  gained  by  a  study  of 
types  with  others  which  can  be  readily  interpreted  by  means 
of  the  experience  in  the  laboratory.  References  from  the 
bare  directions  of  Appendix  I  to  the  paragraphs  and  figures 
of  the  text  are  abundant  and  are  intended  to  aid  the  student 
in  the  comprehension  of  the  type  under  observation.  It  may 
be  objected  that  he  is  thus  aided  too  much.  But  I  believe 
that  in  his  first  steps  in  laboratory  training  the  student  re- 
quires a  large  amount  of  help,  and  that  its  results  are  more 
often  nullified  by  too  little  assistance  than  by  too  much. 

In  the  text  I  have  neither  sought  nor  avoided  the  use  of 
technical  terms.  I  have  refrained  from  making  the  book  a 
mere  illustrated  glossary.  Yet  I  see  no  advantage,  even  for 
young  students,  in  repeated  circumlocution,  for  which  a 
single  word  might  stand.  Definitions  of  most  of  the  tech- 
nical terms  used  may  be  found  by  means  of  the  index  ; 
others  are  defined  in  the  standard  dictionaries.  The  careful 
teacher  will  insist  upon  a  clear  understanding  of  the  meaning 
of  terms  and  the  accurate  use  of  language. 

I  have  refrained  from  frequent  citation  of  plants  by  name 
as  examples  of  facts  stated,  chiefly  because  beginners  are 
rarely  familiar  with  any  plants  except  the  commonest  domes- 
ticated ones  and  a  few  forest  or  shade  trees. 


VI  PREFACE. 

No  apology  is  necessary  for  the  exclusive  use  of  the  metric 
system.  If  pupils  lack  familiarity  with  it,  the  actual  handling 
of  metric  measures  and  weights  will  soon  remedy  this.  A 
useful  chart  showing  the  units  may  be  obtained  of  the  Ameri- 
can Metrological  Society,  41  East  Forty-ninth  Street,  New 
York,  for  ten  cents. 

Very  few  of  the  illustrations  are  original.  In  the  main  they 
have  been  selected  from  a  wide  range  of  standard  works  with 
especial  care  to  secure  accuracy  and  clearness.  Whenever 
possible  the  source  of  the  figure  and  its  magnification  have 
been  given.  The  attention  of  the  teacher  is  invited  to  the 
very  full  description  which  accompanies  each  figure.  In 
these  explanations  will  be  found  much  matter  which  is  often 
put  into  subordinate  paragraphs  in  other  books.  I  have  ob- 
served that  students  are  prone  merely  to  "  look  at  "  figures, 
and  rarely  study  them.  I  therefore  suggest  that  real  study  of 
the  illustrations  as  supplementing  the  text  be  insisted  upon. 
Sections  are  apt  to  be  puzzling  to  beginners  unless  they  are 
taught  how  to  interpret  them.  This  can  be  done  by  requir- 
ing them  to  sketch  on  paper  or  blackboard  imaginary  sections 
of  common  objects  in  different  planes.  Articles  of  regular 
form,  such  as  a  pencil,  book,  slate,  ink  bottle,  desk,  etc., 
may  be  ''sectioned,"  until  from  sketches  of  sections  in  three 
planes  at  right  angles  the  student  can  construct  a  mental 
image  of  the  object. 

Although  divided  into  four  parts,  it  has  not  been  possible 
to  keep  the  subject  matter  of  each  wholly  distinct,  since 
morphology,  physiology  and  ecology  are  so  interrelated.  In- 
deed it  has  been  thought  best  to  combine  the  morphology 
and  physiology  of  the  reproductive  organs  to  form  Part  III, 
rather  than  to  divide  it  between  two.  The  teacher  will  do 
well  to  see  that  the  pupil  does  not  neglect  the  abundant  cross 
references. 

While  the  whole  book  is  simply  a  restatement  of  widely 


PREFACE.  VI 1 

known  facts,  for  which  I  am  mainly  indebted  to  general 
treatises,  monographs  and  shorter  papers,  I  am  constrained 
to  acknowledge  for  Part  IV  my  special  indebtedness  to 
Warming's  Lehrbuch  der  bkologischen  Pflanzengeographie  and 
Ludwig's  Lehrbuch  der  Pjlanzenbiologie. 

C.  R.  B. 
University  of  Chicago. 


CONTENTS. 


Preface 


PAGE 

,     iii 


PART    I:    THE    PLANT    BODY. 


Introduction  :  The  unit  of  structure 
Chapter  I.  Single-celled  plants  and  colonies 
II.  Linear  and  superficial  aggregates 

III.  The  thallus  of  the  higher  alg^e  . 

IV.  The  fungus  body  of  hyphal  elements 
V.  Liverworts  and  mosses 

VI.  Fernworts  and  seed  plants 
VII.  The  root      .... 
VIII.  The  shoot    .... 
IX.  The  stem       .... 


X.  The  leaves 


17 
26 
39 
49 
60 
65 
82 
96 
"7 


PART    II  :     PHYSIOLOGY. 


Chapter  XL  Introduction  :   The  unit  of  function 
XII.  The  maintenance  of  bodily  form 

XIII.  Nutrition 

XIV.  Growth 

XV.  The  movements  of  plants 


M3 

147 
151 
178 

18S 


PART    III:    REPRODUCTION. 


Chapter  XVI.  Introduction  :  Reproductive  structures  .  209 
XVII.  Vegetative  reproduction     .         .         .        .211 

XVIII.  Sexual  reproduction 268 

ix 


CONTENTS. 


PART    IV  :    ECOLOGY. 

PAGE 

Chapter  XIX.  Forms  of  vegetation 30S 

XX.  Mesophytes 312 

XXI.  Xerophvtes  and  halophytes        .         .         .  318 
XXII.   Hydrophytes 327 

XXIII.  Adaptations  to  other  plants  as  supports   330 

XXIV.  Symbiosis 333 

XXV.  Animals  as  food,  foes,  or  friends      .         .  342 

XXVI.   Protection    and    distribution    of    spores 

and  seeds 352 

Appendix  I.  Directions  for  laboratory  study  .        .        .  369 
II.  Directions    for   collecting   and   preserving 

material 401 

III.  Apparatus  and  reagents 409 

IV.  Reference  books 413 

V.  Outline  of  classification        ....  415 

Index 4*9 


PLANT    LIFE. 


PART  I:  THE  PLANT  BODY. 

INTRODUCTION. 

1.  Units  of  structure. — An  examination  of  any  plant  by 
proper  methods  reveals  the  fact  that  it  is  made  up  of  one  or 
more  units  of  structure.  The  unit  of  structure  of  a  brick 
wall  is  the  individual  brick.  Each  has  a  definite  shape  and 
relation  to  others,  upon  which  the  form  of  the  wall  depends. 
The  unit  of  structure  of  a  plant  is  called  a  cell.  The  cells 
have  each  a  definite  form  and  relation  to  others,  and  upon 
these  two  factors  the  form  of  the  entire  plant  depends. 

But  between  the  plant  and  the  brick  wall  there  is  this  im- 
portant difference.  The  bricks,  after  being  perfectly  formed, 
were  put  together.  The  cells  of  the  plant  are  produced  where 
they  lie  and  gradually  groiv  to  a  mature  form  and  size.  The 
bricks  are  originally  disconnected  ;  the  plant-cells  are  con- 
nected by  origin,  and  only  as  they  become  mature  do  they 
separate,  if  at  all. 

2.  The  cell. — A  plant-cell  is  a  minute  portion  of  living 
matter,  called  protoplasm  or  plasma,  generally  surrounded  by 
a  membrane,  called  the  cell-wall  (fig.  i).  If  the  brick  in 
the  previous  illustration  be  taken  to  represent  the  protoplasm, 
the  mortar  may  be  considered  as  the  cell-wall. * 

*  This  illustration  must  lie  carried  no  further  than  to  show  the  relation 
of  position  of  these  two  parts  of  a  cell. 


2  PLANT  LIFE. 

3.  Protoplasm. — The  protoplasm  is  the  essential  part  of 
the  cell.  It  constructs  the  cell-wall.  Rarely,  if  ever,  is  it 
uniform  throughout,  but  is  differentiated  into  distinct  mem- 
bers, each  having  special  work  to  do.  In  the  most  com- 
pletely differentiated  active  cells  the 
greater  part  of  the  protoplasm  con- 
sists of  a  finely  granular  or  nearly 
transparent,  colorless  portion,  called 
cytoplasm.  Embedded  in  the  cyto- 
plasm are  the  nucleus,  centrospheres 
(figs,  i  and  2),  and  plastids  (figs. 
3  to  8). 

Fig.  i.-a  ceil  (the  megaspore)  4.  Cytoplasm.  —  This  is  not  a 
^anuiar'protopiasm^'^vvhich  single  substance,  but  a  mixture  of 
L^tnuintnrfnuci:'  several  different  substances,  so  in- 
ce^,^Tn,TheyiVn:  timately  mixed  and  so  unstable  that 
^snfhethcee.rwlnpl^thrtehPosee'  it  is  not  possible  to  analyze  it. 
eltheMaadinffiend  "oo  diam!-   Moreover,    the   nature   and    amount 

After  Gufgnard.  Qf     tj]e       components      are      probably 

variable.  Most  of  the  substances  belong  to  the  class  of  com- 
pounds called  proteids,  so  that  cytoplasm  responds  to  proteid 
tests  and  is  often  spoken  of  as  a  mixture  of  proteids.  In 
addition  there  are  frequently  present  other  organic  substances 
(such  as  amides,  carbohydrates,  fats,  and  enzymes),  and 
always  small  quantities  of  mineral  matters  which  appear  as 
ash  when  cytoplasm  is  completely  burned.  The  minute 
granules  embedded  in  the  cytoplasm  are  of  various  nature. 
Most  of  them  are  solid  substances. 

5.  Vacuoles. — Scarcely  distinguishable  from  these  at  first 
are  the  minute  cavities,  called  vacuoles,  filled  with  dilute 
watery  solutions  of  many  different  substances,  the  cell- sap. 
In  all  but  the  youngest  cells  more  or  fewer  of  these  bubbles 
of  water  may  unite  to  form  larger  ones  (fig.  7).  These  often 
increase  so  as  to  occupy  the  greater  part  of  the  space  within 


INTKODLCI/O.V.  3 

the  cell-wall,  being  separated  only  by  plates  of  protoplasm. 
When  all  vacuoles  fuse  into  one  the  cytoplasm  is  crowded  as 
a  thin  layer  against  the  wall,  with  sometimes  strands  of  it 
crossing  the  vacuole  as  the  remnants  of  the  plates  at  an 
earlier  stage  (fig.  188). 

6.  Nucleus. — The  nucleus  varies  much  in  shape.  In  cells 
whose  diameters  are  nearly  equal,  it  is  generally  spherical 
or  ovoid,  but  in  elongated  cells  it  may  become  spindle- 
shaped  or  cvlindric.  It  is  surrounded  by  a  very  delicate 
membrane,  and  is  composed  of  two  sorts  of  substances,  one 
of  which  can  be  readily  stained  by  certain  liquid  dyes,  while 
the  other  usually   remains  uncolored  (fig.  2).     The  nucleus 


Fig.  2. — A  part  of  the  same  cell  as  in  fig.  i,  but  older,  with  the  nucleus  beginning  to 
divide.  The  dark  thread  in  A,  separated  into  pieces  in  />.  represents  the  chroma 
tin  of  the  nucleus  deeply  stained,  the  rest  of  the  nuclear  material  being  unstained. 

a,  centrospheres.     Magnified  f diam. — After  Cuignard. 


may  divide  into  two,  a  regular  succession  of  changes  in  the 
arrangement  of  the  materials  composing  it  characterizing  this 
process,  which  is  commonly  followed  by  the  formation  of  a 
partition-wall  separating  the  cell  into  two  parts,  each  con- 
taining one  of  the  daughter-nuclei. 


4  PLANT  LIFE. 

7.  Centrospheres. — The  centrospheres  are  intimately  re- 
lated to  the  nucleus.  They  are  two  very  minute  spherical 
bodies  lying  in  contact  with  it  (figs,  i,  2).  When  the 
nucleus  is  about  to  divide  one  centrosphere  goes  to  each 
pole  (fig.  2,  B),  and  the  separation  of  the  nuclear  material 
occurs  near  the  nuclear  equator.  Just  as  this  occurs  the 
centrospheres  divide,  forming  a  pair  at  each  pole.  Two 
accompany  each  daughter-nucleus.  Their  purpose  is  not 
yet  fully  understood. 


•••28 


Fig. 


Fig. 


Fig. 


t,  showing  its 


wall,  and  some 
il-drop.     Mag- 


Fig.  3. — A  cell  from    the    interior  of   the  leaf  of  the 
inclusions  of  the  cytoplasm,     z,  the  nucleus;  c,  chloropla 
nified  about  ioo  diam  —After  Zimmermann. 

Fig.  4. — A,  chloroplasts  from  the  skin  of  the  petiole  of  ivy;  B,  from  the  inner  leaf- 
cells  of  morning-glory;  C,  from  the  same  cells  of  Achyranthes.  The  shaded  parts 
are  protoplasm  in  which  are  embedded  starch-granules,  j,  and  proteid  crystalloids, 
k.     Magnified  about  iooo  diam. — After  Zimmermann. 

Fig.  5.- — Leucoplasts  from  a  young  shoot  of  Canna.  The  shaded  part  is  protoplasm, 
in  which  are  embedded  starch-grains,  s,  and  proteid  crystalloids,  k.  Magnified 
about  1000  diam. — After  Schimper. 


8.  Plastids. — In  most  cells  there  are  also  other  protoplas- 
mic structures,  the  plastids.  In  young  cells  these  are  small, 
rounded,  colorless  bodies.  As  the  cell  grows  older  they  in- 
crease in  size  and  number.  At  maturity,  in  cells  which  lie 
near  the  surface  of  green  plants,  they  are  commonly  roundish 
or  biscuit-shaped,  of  spongy  texture,  and  colored  yellowish- 


IN  TROD  UC  TION.  5 

green  by  a  substance  known  as  chlorophyll.  These  are  con- 
sequently known  as  chloroplasts  or  chlorophyll-bodies  (figs. 
3,  4).  In  other  cells,  particularly  those  for  the  storage  of 
food,  they  may  develop  into  smaller,  denser,  flattened  or 
roundish,  uncolored  bodies,  called  leucoplasls  (figs.  5,  6,  7). 
These   may   act   either   as   starch-accumulators,    or    in  case 


Fig.  6. 


Fig.  7. 


Fig.  6.— Part  of  the  cell-contents  of  an  inner  cell  of  white  potato,  z,  nucleus;  j, 
starch-grains,  each  having  been  formed  by  a  leucoplast,  /,  which  is  still  attached  to 
one  side  of  the  grain;  k,  crystalloid.  Magnified  abont  iooo  diam. — After  Zimmer- 
mann. 

Fig.  7.— Leucoplasts  in  place  in  a  young  cell  of  a  leaf  of  vanilla.  /,  leucoplasts;  z, 
nucleus;  e,  an  oil-former  or  elaioplast.  The  unshaded  spaces  surrounded  by  proto- 
plasm are  vacuoles.     Magnified  about  1000  diam. — After  Wakker. 

of  need,  in  young  cells,  may  even  be  converted  into  chloro- 
plasts. In  other  cells,  particularly  in  highly  colored  parts, 
the  plastids  may  become  of  most  diverse  form  and  size,  and 
colored  red  or  yellow,  whence  they  are  called  chromoplasts 
or  color-bodies  (figs.  8,  9). 

9.  Wall. — The  cell-wall  is  formed  by  the  protoplasm. 
In  green  plants  when  first  formed  it  consists  chiefly  of  cell- 
ulose, with  which,  as  it  grows  older,  various  other  substances 
may  be  mixed.  Some  of  these,  such  as  pectin,  are  present 
even  in  the  young  wall,  and   may  increase  with  age;  others 


O  PLANT  LIFE. 

are  characteristic  of  special  changes  which  the  wall  may 
undergo.  The  most  noticeable  changes  are  four:  (i)  Some 
cell- walls  contain  suberin  or  cutin,  fat-like  substances  by  the 
presence  of  which  water  and  gases  are  hindered  from  passing 


Fig.  8.  Fig.  9. 

Fig.  8.— I,  chromoplasts  from  flower-leaves  of  an  orchid;  II,  from  the  root  of  carrot; 
III,  from  the  fruit  of  mountain-ash.  Embedded  in  the  protoplasmic  body  of  the 
chromoplast  are  sometimes  proteid  crystalloids,  /,  pigment-crystals,  _/",  or  starch- 
grains,  j.     Magnified  about  1000  diam. — After  Schimper. 

Fig.  9.  — Chromoplasts  from  the  flesh-colored  shoots  of  the  horsetail,  containing  the 
coloring  matter  in  the  form  of  granules  embedded  in  colorless  protoplasm.  Mag- 
nified 1400  diam. — After  Zimmermann. 

through.  The  cell-walls  of  bottle-cork  are  suberized,  and 
those  in  the  skin  of  the  apple  are  cutinized.  (2)  Some  cell- 
walls  are  lignified,  as,  for  example,  those  of  wood  by  reason  of 


Fig.  io.— A  part  of  a  thin  slice  lengthwise  through  the  centre  of  the  stem  of  garden- 
balsam.  The  cells  and  vessels  are  elongated  and  are  here  seen  from  the  side,  show- 
ing the  thickened  lines  on  the  side  walls  of  v,  v',  v",  v"\  v"",  and  v'"".  Mag- 
nified about  400  diam. — After  Duchartre. 

the  presence  of  certain  substances  (vanillin,  coniferin,  etc.). 
They  allow  the  ready  passage  of  water  and  gases.  (3)  Others 
are  so  transformed  that,  in  contact  with  water,  they  swell 
enormously,   forming  a  mucilage  or  gum.     These  swelling 


INTRODUCTION. 


substances  are  produced  by  the  alteration  of  the  cellulose  or 
other  constituents  of  the  original  wall.  (4)  An  excessive 
deposit  of  mineral  matters  in  tin 
wall  is  known  as  mineralization 
Such  walls  may  even  retain  their 
form  after  all  organic  matter  is 
burned  out,  as  in  the  skin  of  the 
scouring  rush  or  horsetail. 

10.  Growth  of  the  cell-wall. — 
As  the  cells  become  older  the  wall 
may  increase  in  thickness.  It  must 
also  increase  in  area  as  the  cells 
grow  in  size.  The  growth  in  area 
is  usually  accomplished  by  putting 
new  particles  between  the  older 
ones.  Growth  in  thickness  is  rarely  F 
uniform.  When  the  wall  grows 
thicker  except  at  certain  spots,  these 
remain  as  pits  or  pores  in  the 
thickening  layers.  When  only  cer- 
tain   spots    or    lines    grow    thicker, 

the  wall   shows  projecting   spikes,  bands,  or   threads,    which 
give  it  the  appearance  in  figs.  10,  n. 


c  11.  —  Cells  from  a  liverwort 
showing  thickened  walls  A, 
half  an  elater;  A',  a  part  more 
highly  magnified;  B,  a  cell  from 
the  lower  part  of  the  thallus, 
with  reticulate  thickenings 
(shaded);  C,  D,  rhizoids  with 
isolated  branched  thickenings. 
Highly  magnified.  —  After 
Sachs. 


CHAPTER    I. 


SINGLE-CELLED    PLANTS    AND    COLONIES. 

In  the  lakes  and  pools,  in  ditches  and  slow  streams,  on 
the  surface  of  damp  rocks  and  wood,  may  be  found  many 
sorts  of  microscopic  plants,  whose  entire  body  is  merely  a 
single  cell. 

Blue-green  algae. 

11.  Fission-algse. — The  simplest  forms  of  these,  the  fission- 
algae,  have  the  protoplasm  only  slightly  differentiated.  The 
central  part  becomes  the  nucleus,  while  the  whole  of  the 
remaining  protoplasm  is  colored  by  the  chlorophyll  and  a 
blue  coloring  matter  called  phycocvanin,  so  that  in  mass  these 
algae  look  bluish-green  or  even  blackish.  For  this  reason 
they  are  called  blue-green  algae  to  distinguish  them  from  those 
in  which  only  the  yellow-green  of  chlorophyll  is  present. 

12.  Gelatinous  colonies. — The  cell-wall  may  be  a  thin 
sheet  of  cellulose,  but  commonly  it  is 
composed  of  several  layers,  of  which 
the  outer  are  changed  into  mucilage. 
This  swells  into  a  transparent  jelly 
when  wet,  either  becoming  homo- 
geneous or  showing  distinct  stratifica- 
tion. When  a  number  of  such  forms 
grow  in  company  (fig.  12),  this 
jelly-like  material  blends  into  a  single 


plants    seems    to    be  em- 


Fig.  12—  A  blue-preen  aljra 
(Gl(roca/>sa<.  Single  indi- 
viduals,   A,     and     colonies 

\S'E)r  °a     varous    wfs   associated 

Magnified  300  diam. — After 

Sachs-  bedded. 

13.  Gelatinous  filament-colonies. — In  other  cases,  instead 
of  being  associated  only  by  the  adhesion  of  the  mucilaginous 
portion  of  the  cell-wall,  the  cells,  still  practically  inde- 
pendent the  one   of  the  other,    remain    connected    by    the 


SINGLE-CELLED    PLANTS   AND    COLONIES. 


firmer  portions  of  the  wall  into  rows,  forming  irregularly 
coiled  or  serpentine  filaments,  which  are  embedded  in  a 
profuse  gelatinous  material  (fig.  13).  The  essential  inde- 
pendence of  the  individual  cells,  even  though  they  remain 
connected,  is  shown  by  the  fact  that  such  a  chain  may  be 


)       8 


tKf? 


Fig.  13. — Nostoc.  A.  a  gelatinous  colony,  irregularly  lobed.  Natural  size.  B,  a 
portion  of  a  serpentine  filament  with  five  heterocysts  (one  at  each  end  by  which  it 
was  separated  from  the  rest  of  the  cells  composing  the  filament,  and  three  inter- 
mediate ones)  and  the  jelly  belonging  to  it.  Magnified  about  400  diam. — After 
Thuret  and  Janczewski. 


broken  up  into  any  number  of  pieces  and  each  piece  will 
retain  all  its  powers.  Here  and  there  in  the  chain  there 
occur  cells  unlike  the  rest  (Ji,  fig.  14),  called  heterocysts, 
whose  function  seems  to  be  to  break  the  chain  into  pieces, 
from  the  growth  of  which  independent  colonies  may  arise. 
The  association  of  considerable  numbers  of  these  plants  in 
colonies  gives  rise  to  masses  of  jelly  which  vary  from  the  size 
of  a  pin-head  to  2-5  centimeters  in  diameter.  They  may  be 
found  adhering  to  water-weeds  as  clear-  or  dirty-green 
masses,  or  sometimes  floating  free   (-/,  fig.  13). 

14.  Filaments  of  loose  organization. — Of  very  near  kin 
to  these  plants  are  the  oscillarias,  which  have  received  this 
name  from  the  pendulum-like  swinging  of  their  tips  (fig.  15). 
In  them  the  cells  remain  connected  more  extensively  and 
more  firmly,  so  that  each  is  disk-shaped,  and  the  filament  is 
much  less  easily  separated  into  its  component  cells.      More- 


[O 


PLANT  LIFE. 


over  the  gelatinous  part  of  the  wall  is  much  less  prominent, 
so  that  often  it  is  only  seen  with  difficulty.  Even  though 
invisible,  it  may  be  detected  by  the  slippery  feel  of  the 
plants  when  rubbed  gently  between  the  fingers. 


Fig.  15. 

Fig.  14. — Part  of  a  filament  ol  A  nab  ana.  h,  heterocyst;  a-d,  successive  stages  in 
the  division  of  a  cell  of  the  filament.     Magnified  540  diam. — After  Strasburger. 

Fig.  15. — Oscillaria.  a,  the  tip;  b,  a  portion  of  the  middle  of  a  filament.  Magnified 
540  diam. — After  Strasburger. 

15.  Feeding  habits. — The  feeding  habits  of  the  oscil- 
larias  are  worth  notice.  They  are  found  in  permanent 
puddles  and  ditches  where  organic  matter  is  decaying.  The 
significance  of  this  is  that  some  of  the  ancestors  of  the  green 
oscillarias  probably  had  offspring  which,  instead  of  living 
upon  food  prepared  by  means  of  the  green  coloring  matter 
(see  ^[  230),  learned  to  utilize  the  organic  matter  in  the 
water,  at  first  perhaps  no  more  than  the  present  oscillarias 
do  ;  but  gradually  they  came  to  live  exclusively  upon  it. 
As  a  consequence,  they  lost  their  color  and  became  incapable 
of  existing  where  organic  food  cannot  be  had. 

Bacteria. 

16.  Fission-fungi. — Along  with  the  loss  of  color  and 
change  of  habit  went  a  diminution  in  size.     They  have   thus 


SINGLE-CELLED    PLANTS  AND    COLONIES.        II 

become  so  different  that  they  are  now  known  as  fission-fungi, 
and  popularly  as  bacteria,  bacilli,  microbes,  germs,  etc. 
These  plants,  probably  the  descendants  of  common  ancestors 
with  the  fission-algae,  are  the  smallest  known  organisms 
(figs.    1 6,    17).       The     diameter    of   many    sorts    does    not 


4?V 


0      VSf\ 

%|| 

gC 

©      % 

Fig.  16. — Various  bacteria,  a,  Micrococcus,  the  "  blood-portent"  ;  i,  zoogloea  form 
of  the  same  ;  c.  Bacterium  aceti,  the  ferment  of  vinegar  ;  </,  Sarcina,  a  harmless 
parasite  of  the  human  intestine,  a,  /',  magnified  300  diam.;  c,  2000  diam.;  </,  800 
diam.— After  Kerner. 

exceed  .0005  of  a  millimeter.  That  would  allow  175  to 
lie  side  by  side  upon  the  edge  of  the  paper  on  which  this 
book  is  printed.  In  many  the  successive  divisions  are 
parallel,  in  others  they  divide  the  cells  in  two  planes,  ami  in 
others  again  in  three.  The  cells,  when  they  divide,  separate 
readily,  in  most  sorts  never  cohering  at  all,  but  living  as 
independent  cells  as  soon  as  produced.  Other  sorts  remain 
connected  into  two-  to  several-celled  chains,  sheet,  or  packets 
(a,  d,  fig.   16).      A  few  have  their  cells  firmly  coherent   into 


PLANT  LIFE. 


a  filament.  As  the  cells  are  either  spherical  or  rod-like,  the 
shape  of  the  colony  depends  upon  the  shape  of  the  compo- 
nent cells  and  the  way  in  which  they  divide  (see  ^[  24). 

17.  Gelatin. — In  the  fission-fungi,  as  in  the  fission-algae, 
considerable  masses  of  gelatinous  material  are  produced,  in 
which  the  cells  may  lie  embedded.  The  films,  sometimes 
smooth,  sometimes  wrinkled,  which  appear  on  an  infusion  of 
organic  matter,  are  formed  by  the  masses  of  bacteria  which 
become  embedded  in  the  gelatinous  material  produced  by 
the  alteration  of  their  cell-walls  {b,  fig.  16). 

18.  Cilia. — Most  species  are  furnished  with  locomotor 
organs  consisting  of  fine  threads  of  cytoplasm  protruded 
through  the  wall,  which,  by  their  sudden  contraction  on  one 
side,  lash  about  like  whips,  and  propel  the  cell  by  jerky, 
darting  motions  through  the  fluid  in  which  it  swims.  These 
lashes,  called  cilia,  may  be  single  at  the  ends  of  the  cell 
(C,  fig.  17),  or  many  at  ends  or  sides  (A,  fig.  17),    or  the 

It  *   \\ 

0 

Fig.  17. — Bacteria  stained  to  show  cilia.  A,  cilia  tufted  at  one  end;  />',  cilia  irregu- 
larly distributed  over  body;  C,  cilium  single  at  one  or  both  ends.  B.  the  bacillus 
of  typhoid  fever;  C,  the  bacillus  of  Asiatic  cholera.  Magnified  775  diam.— After 
Migula. 

whole  cell  may  be  covered  with  them  like  hairs  (B,  fig.  17). 
They  may  be  withdrawn  or  drop  off  when  the  plant  comes 
to  rest,  as  when  they  form  the  scums  previously  mentioned. 

These  plants  are  most  interesting  on  account  of  their 
economic  relation  to  health  and  disease,  decay,  fermentation, 
etc.,  which  cannot  be  discussed  here.* 

*  For  further  information  on  these  plants,  see  Frank/and ;  Our 
Secret  Friends  and   Foes ;  Prudden :  Story  of  the   Bacteria,  Dust  and 


SINGLE-CELLED    PLANTS   AND    COLONIES. 


13 


Yellow-green  algae. 
19.   Single-celled  plants  with  chloroplasts.— Among  the 
single-celled  green  plants,  one  of  the  most  common  groups 


Fig.  18. — Pleurococcus  viridis.     A,  a  single   individual;   B,  a  colony  shortly  after 
division;  C,  the  same  after  separation.     Magnified  540  diam. — After  Strasburger. 

is  that  represented  by  fig.  18,  which  shows  a  representative 
of  an  extensive  series  in  which  the  vegetative  body  consists 
of  a  single  cell  with  its  wall,  cyto- 
plasm, nucleus,  and  a  few  relatively 
large  chloroplasts.  In  this  greater 
specialization  of  the  protoplasm,  these 
plants  show  the  only  ■  advance  upon 
the  blue -green  algae.  The  wall  in 
such  as  this  Pleurococcus  is  almost 
uniform  and  quite  thin. 

20.   Colonies. — The    cells   are   fre- 
quently   associated    in 
bedded   in  jelly  or   not.      The   most 
striking  and   elaborate  of  these  colo- 
nies is  formed  by   Volvox  (fig.  19). 

In  this  plant  the  colony  is  a  hollow 
sphere,  often  large  enough  to  be  seen 
by  the  naked  eye  as  a  minute  green  ball,  composed  of  thou- 
sands of  individuals,  embedded  in  a  common  jelly,  arranged 
in  a  single  layer  at  the  surface.  Each  is  connected  with  its 
immediate    neighbors    by   strands  of    protoplasm,    and    two 

its  Dangers,  Drinking-water  and    Ice  Supplies  ;   Russell:    I 'airy  Bacteri- 
ology; Frankel  (tr.  by  Linsley)  :    Bacteriology  (medical). 


1       •  Fig.    iq. — Volvox. 

colonies,    em-    -ni,  individuals 


olony. 

repre- 
sented by  the  minute  circles, 
between  which  the  protoplas- 
mic strands  form  a  network. 
The  large  balls  in  the  interior 
are  daughter-colonirs  to  be 
set  free  upon  the  rupture  and 
death  of  the  mother-colony. 
Magnified  about  45  diam. — 
From  Bessey. 


U 


PLANT  LIFE. 


cilia  are  protruded  into  the  water  outside.  The  lashing  of 
these  rolls  the  whole  colony  about.  Each  vegetative  in- 
dividual is  entirely  like  the  others,  but  those  connected 
with  reproduction  become  specialized. 

Diatoms  and  desmids. 
21.   Shelled  plants. — Other  one-celled  plants  constitute  a 
group  known  as  diatoms,  found  in  both  fresh  and  salt  waters, 
a  b  c  d 


Fig.  20. — Various  diatoms,  a,  Synedra  ;  6,  Pleurosigma  :  c,  d,  GrammatofiAora, 
side  and  top  views  ;  c.  colony  of  Gomfihonema,  with  branched  stalks  attached  to  an 
alga;y,  g,  single  cells  of  same,  more  magnified,  top  and  side  views;  A,  colony  of 
Diatoma,  ihe  cells  connected  into  a  zigzag  band  ;  t,  k,  colony  and  individuals  (top 
and  side  views)  of  Fragillaria  :  /,  «/,  >i,  Cocconema.  In  m  the  pair  is  surrounded 
by  jelly  preliminary  to  the  escape  of  the  protoplasm  and  the  formation  of  two  new 
cells  (auxosporesi  which  has  been  completed  in  «.— After  Kerner. 

either  attached  or  free-swimming  (figs.  20,  21).  The  dia- 
toms are  very  various  in  form,  and  present  two  different 
aspects.  When  seen  from  the  side  they  are  generally  elon- 
gated-rectangular. When  looked  at  from  above  they  are 
short-cylindric,  disk -shaped,  boat -shaped,  or  variously  curved 


S1XGLE-CELLED    PLANTS  AND    COLONIES.        15 

or  angular.  They  are  peculiar  in  having  the  cell-wall  so  im- 
pregnated with  silica  that  scarcely  any  organic  matter  is  left. 
Indeed  the  plants  may  be  heated  to  a  red  heat  and  boiled  in 
acid  without  destroying  the  form  and  markings  of  the  cell- 
wall,  so  completely  has  it  become  silicified.  To  permit 
growth  this  rigid  cell-wall  is  constructed  in  two  pieces  which 
fit  together  like  the  two  parts  of  a  pill-box  (fig.  21).  Each 
of  these  pieces,  or  valves,  is  sculptured  into  regular  patterns 
in  lines  and  dots,  which  are  often  so  excessively  minute  or 
close  together  as  to  be  barely  visible  with  the  highest  powers 
of  the  microscope  (b>  fig.  20).  Seen  in  mass,  as  they  may 
often  be  on  the  sides  of  a  glass  aquarium,  living  diatoms 
appear  yellowish-brown.  The  chloroplasts,  which  are  some- 
times single  and  always  few,  contain  a  brownish  pigment 
(dia/omin)  in  addition  to  the  green  chlorophyll. 


Fig.  2i. — A  single  diatom  (Navicula  amphirhynchus).  A}  top  view  ;  />,  side  view, 
showing  overlapping  of  the  valves.  The  parts  shaded  by  lines  are  the  chloroplasts; 
the  dotted  part  the  protoplasm,  with  nucleus  about  the  center  of  cell.  Magnified 
750  diam. — After  Pfitzer. 

It  is  not  uncommon  for  the  diatoms  to  form  colonies  by 
the  adhesion  of  several  or  many  individuals  by  means  of 
gelatinous  cell-walls.  These  colonies  are  ribbon-like,  or  zig- 
zag chains,  or  even  branched  filaments  (//,  i,  fig.  20). 
Other  sorts  may  be  attached  singly  or  in  clusters  by  a  gelati- 
nous stalk  (e,  fig.  20).  In  all  cases  the  jelly,  like  the  rest 
of  the  cell-wall,  is  a  product  of  the  protoplasm.     The  slow 


[6 


PLANT  LIFE. 


gliding  movements  of  some  free  diatoms  are  due  to  the  pro- 
trusion of  strands  of  cytoplasm  through  slits  in  the  valves. 

22.  The  desmids. — These  form  another  group  of  one- 
celled  green  alga;.  They  have  neither  the  brownish  color 
nor  siliceous  wall  characteristic  of  diatoms,  but  are  bright 
green  cells  of  remarkably  diverse  and  often  beautiful  forms. 
As  a  rule  the  cell  is  flattened  and  is  divided  almost  into  two 
by  a  deep  constriction  near  the  middle  (a,  b,  c,  e,  fig.  22). 


Fig.  22. — Various  desmids.  a,  Micrasterias  ;  6,  Cosmarium  ;  c,  Xanthidium  ; 
d,  Closterium  ;  f,  Staurastrum  ;  J,  Aptogonum.  Magnified  about  200  diam. 
—  After  Kerncr. 


Often  the  body  of  the  cell  is  covered  with  warts  or  spine-like 
projections  (b,  c,  fig.  22),  or  is  prolonged  into  horn-like  or 
hair-like  lobes.  These  plants  also  frequently  cohere  into 
colonies  (_/",  fig.  22).  In  that  case  tooth-like  projections  of 
the  cell-wall  may  interlock. 


CHAPTER    II. 

LINEAR  AND  SUPERFICIAL  AGGREGATES. 


Obviously  some  of  the  plants  mentioned  in  the  last  chapter, 
such  as  the  oscillarias,  are  colonies  of  cells  well  on  the  way 
to  complete  union  into  coherent  filaments  whose  elements  are 
attached  to  each  other  by  considerable  areas  of  the  cell-wall. 
In  order  clearly  to  understand  this  condition,  we  must  con- 
sider the  mode  of  origin  of  the  individual  cells  composing 
the  row. 

23.  Fission. — Under  conditions  unknown  to  us,  in  the 
course  of  its  growth  a  cell  may  divide  by  a  process  known 


Fig.  22A. — A,  one  of  the  final  stages  in  cell-division.  The  daughter-nuclei  are  still 
connected  by  kinoplasmic  filaments,  and  across  the  equatorial  plane  particles  of  new 
cell-wall  material  are  formed.  A',  the  completion  of  cell-division;  the  daughter- 
nuclei  have  rounded  off  and  the  new  wall  is  like  the  lateral  walls.  Magnified  880 
diam. — After  Strasburger. 


Fig  22B.— Three  stages  of  division  in  the  same  cell  of  an  orchid  (£pipactis 
palustris).  The  cell  is  occupied  in  great  part  by  vacuoles,  [n  this  case  the  new 
wall  forms  first  on  one  side  between  tin-  nuclei  (.! ),  which  gradually  travel  across 

to   the   opposite   side  (A),  the  wall   extending  until   it   is  complete  (O.      Magnified 
about  380  diam. — After  Treub. 

17 


1 8  PLANT  LIFE. 

as  fission.  The  material  of  the  nucleus  passes  through  a 
complex  series  of  changes  and  separates  into  two  parts.  In  a 
plane  between  these  daughter-nuclei  particles  are  deposited 
to  form  a  cell- wall  (A,  fig.  22A).  The  formation  of  the 
partition-wall  may  occur  simultaneously  in  all  parts,  or  it  may 
be  formed  on  one  side  first  and  the  nuclei  move  across  the 
cell  until  it  joins  the  lateral  walls  (fig.  22B).  In  this  way  an 
isolated  unicellular  plant  of  Pleurococcus  (A,  fig.  18)  may 
divide  into  two  cells  so  that  it  consists  of  two  hemispherical 
cells,  each  capable  of  independent  growth  (fig.  23,  A). 
After  a  time  these  cells  may  separate  from  each  other  by  the 
cracking  of  the  original  wall  at  the  line  of  juncture  with  the 
new  partition  and  the  cleaving  of  this  partition  parallel  to  its 
surfaces  into  two  layers,  one  of  which  covers  a  portion  of 
each  of  the  thus  disconnected  cells  (fig.  18,  C).  If  this 
process  of  division  and  separation  goes  on,  the  result  will  be 
the  production  of  a  number  of  independent  cells  more  or  less 
closely  associated  but  not  connected. 

24.   Cell-rows,    surfaces,    and   masses. — In   many   cases, 
however,  a  second  division  occurs  in  one  or  both  cells  before 


Fig.  23.— Diagrams  of  cell  division.  A,  division  of  a  spherical  cell  into  two  hemi- 
spherical cells,  a,  b,  by  the  wall  i.  />',  the  same  after  further  division  in  planes  2, 
2,  3,  parallel  to  1.  a  has  divided  by  wall  2  into  a'  and  another  cell  which  has  again 
divided  by  wall  3  into  a",  a",  b  has  divided  into  i',  b' ,  the  inner  of  which  has 
elongated  preparatory  to  a  division  into  b",  b" ,  as  by  wall  3.  C,  fig.  A  after  a 
second  division,  by  wall  2,  at  right  angles  to  1. 

separation;  and  sometimes  even  a  third  division  takes  place. 
It  is  evident  that  the  position  of  the  later  partitions  deter- 
mines the  form  of  this  temporary  aggregate  of  cells,  (a)  If 
each  of  the  two  divides  in  a  plane  parallel  to  the  first  parti- 


LINEAR  AND    SUPERFICIAL   AGGREGATES.       1 9 

tion,  a  roiv  of  four  cells  will  result;  the  two  inner  cells 
would  be  disks  or  short  cylinders,  while  the  two  outer  would 
be  hemispheres  (fig.  23,  B).  (b)  But  if  (as  is  actually  the 
case  in  Pleurococcus,  B,  fig.  18)  the  new  partitions  are  at 
right  angles  with  the  first,  the  result  is  a  cluster  of  four  cells, 
each  of  which  is  a  quarter  of  a  sphere  (fig.  23,  C). 

Should  a  third  division  occur,  it  is  conceivable  that  the 
new  septa  might  be  placed  parallel  to  those  already  formed, 
in  case  a  ;  or  parallel  to  one  set  and  at  right  angles  with 
the  other,  in  case  b  ;  or  at  right  angles  to  both,  in  case  c. 
In  the  first  instance  there  would  be  formed  a  row,  or  filament, 
of  eight  cells;  in  the  second,  a  sheet  of  eight  cells;  or,  in  the 
third,  a  mass  of  eight  cells.  This  exhausts  the  possibilities  in 
the  position  of  successive  partitions.  If  other  divisions 
occur,  they  will  necessarily  be  more  or  less  nearly  parallel  to 
some  one  of  the  first  three  sets.* 

The  structures  resulting  from  cell-division  where  the  cells 
remain  united  are  conveniently  designated  as  follows:  (1) 
cell-rows,  filaments,  or  linear  aggregates,  arising  by  division 
in  one  plane;  (2)  cell-surfaces,  or  superficial  aggregates, 
arising  by  division  in  two  planes;  (3)  cell-masses,  or  solid 
aggregates,  arising  by  division  in  three  planes. 

It  is  manifest  that  there  are  likely  to  be  all  degrees  of  union 
remaining  between  the  cells  of  linear  and  superficial  aggre- 
gates, and  that  the  extent  and  firmness  of  such  union  will 
depend  largely  upon  the  character  of  the  wall.  As  in  every 
other  case,  the  artificial  distinction  between  cell-colonies  and 
cell -aggregates  is  bridged  by  all  manner  of  intermediate 
forms. 

Filamentous  algae. 

There  is  a  large  number  of  plants  in  which  the  vegetative 
body  throughout  life  has  the  form  of  a  filament.     The  green 
*The  formation  of  partitions  at  angles  other  than  900  or  l8o°  to  pre- 
ceding ones  would   not    affect  the   genera]    result,  luu  would   only  render 
the  form  of  the  product,  as  well  as  of  the  individual  cells,  less  regular. 


20 


PLANT  LIFE. 


plants  of  this  sort  live  almost  entirely  in  water  or  in  wet 
places,  and  may  be  conveniently  designated  as  the  filamentous 
algce. 

25.   Spirogyra,  etc. — Among  these  none  are  more  beautiful 
or  interesting  than  the  filamentous  Conjugate,  represented  in 


Fig.  26. 

Fig.  24. — A    cell  from  filament   of  Sfirogyr-a. 

ch,  chloroplast   (there  are  three  in  this  Veil); 

/,    pyrenoids  ;     k,    nucleus.      Magnified    200 

diam. — After  Straslmrgcr. 
Kig.   25. — A   cell   from    filament   of   Zygnema, 

showing  two  stellate  chloroplasts,  in  each   of 

which  is  a  pyrenoid,  with  the  nucleus  between 

them.     Cytoplasm   poorly  shown.     Magnified 

550  diam. — After  Sachs. 
Fig.  26. — Two  cells  from  filament  of  Zygonema, 

showing  the  gelatinous  sheath  greatly  swollen. 

Magnified  245  diam. — After  Klebs. 


our  waters  by  the  genera,  Spirogyra,  Zygnema,  Mesocarpus, 
and  some  others.*  They  may  be  readily  recognized,  during 
their  vegetative  period,  by  their  unbranched  filaments,  bright 

*To   the    Conjugate   also   belong   tbe    single-celled   desraids   already 
described. 


LINEAR   AND    SUPERFICIAL    AGGREGATES-       21 


green  color,  and  slippery  "  feel ' '  between  the  fingers.*  Under 
the  microscope,  they  are  at  once  distinguished  from  other 
filamentous  algse  by  the  shape  of  their 
chloroplasts.  In  Spirogyra  these  form 
one  or  more  fiattish,  spirally  wound  rib- 
bons, notched  on  the  edges,  and  embedded 
in  the  protoplasm  near  the  cell-wall  (ch, 
fig.  24).  In  Zygnema  there  are  generally 
two  irregularly  star-shaped  chloroplasts 
(figs.  25,  26)  ;  while  in  Mesocarpus  a 
single  flat,  plate-like  chloroplast,  nearly 
as  wide  as  the  cell,  traverses  its  center 
(ng-  27). f 

Embedded  in  the  chloroplasts  of  these 
and  other  algaj  are  usually  seen  one  or 
more  angular,  colorless  bodies,  often  sur- 
rounded by  a  jacket  of  starch.  These  are 
crystals  of  reserve  proteid,  known  aspyre- 
noids  (/>,  figs.  24,  27).  Their  size  depends 
upon  the  amount  of  reserve  food  possessed 
by  .the  plant. 

In  these  plants  there  is  little  or  no  dif- 
ference between  the  parts  of  the  filaments. 
If  broken  into  two,  each  part  may  continue 
growing  with  no  damage  to  any  part 
except  the  cells  which  were  ruptured  in 
severing  the  plant. 

26.  Ulothrix,  etc. — But  other  filamentous  alga?  show  a 
distinction  between  base  and  apex.      In  Ulothrix  (fig.  301) 

*  This  slipperiness  is  due  to  the  gelatinous  outer  part  of  the  cell-wall 
(fig.  26),  which  is  only  visihle  after  special  treatment  or  on  examining  the 
filaments  in  a  thin  mechanical  solution  of  Chinese  ink. 

f  See  also  Ulothrix  (tig.  ?oi),  which  has  in  each  cell  a  single  chloro- 
plast in  the  form  of  a  thick  ring. 


ig.  27.— A  cell  from  fila- 
ment of  Mesocarpus. 
The  darker  body  nearly 
filling  cell  is  the  chloro- 
plasl  (lace  view)  in 
which  are  pyrenoids,  /, 
and  tannin  vesicles,  g. 
1  f  seen  from  a  direction 
at  right  angles  it  would 
appear  as  a  narrow 
stripe  in  the  center  of 
the  cell,  z,  the  nucleus. 
Magnified  about  200 
diam.— After  Zimmer- 


22 


PLANT   LIFE. 


the  basal  cell  is  elongated  and  pointed,  and  is  colorless, 
because  it  is  not  furnished  with  chloroplasts  like  the  others. 
By  this  pointed  cell  the  plant  is  loosely  attached,  at  least 
when  young,  to  the  substratum,  while  the  green  portion 
waves  freely  in  the  water.  Thus  arises  a  distinction  into  two 
parts,  viz.,  the  rhizoid  and  the  thallus. 

In  Cladophora,  Vaucheria,  and  their  allies,  the  plants  are 
generally  attached  by  a  well-developed  rhizoid-region,  which 
is  often  branched  {w,  fig.  28),   as   is  also  the   thallus.     In 


iture 


Fig.   28. — A    young    plant   of   I'aucheria,  developing  from    the   spore.     A, 

:int  further  develop 
ch  it  attaches  itsel 

next  the  wall  on  all  sides 


spore  ;  B,  the  same  after  germination   has  begun  ;   (',  plant  further  developed  from 

hich   it  attaches  itself  to  the 


spore,  s/>,  with   growing  apex,  j,  and  rhizoid,  iv,  by 
mud.     The  chloroplasts  are  numerous  and  close  togetl 
Magnified  28  diam.— After  Sachs. 


contrast  with  the  preceding,  therefore,  localization  of  grmvth, 
producing  branching,  may  be  observed. 

27.  Branching. — A  branch  begins  by  the  growth  in  area 
of  a  limited  portion  of  the  cell-wall.  The  pressure  of  the 
contained  protoplasm  upon  the  wall  causes  it  to  bulge  out- 
ward at  this  point,  and  the  convexity  gradually  increases  as 
the  region  grows  until  the  swelling  becomes  an  outgrowth, 
whose  further  lengthening  constitutes  a  branch  similar  to  the 
main  filament.  Growth  in  length  may  be  limited  to  the  tip 
of  the  filament,  or  to  a  narrow  zone  including  one  or  more 
cells,  or  it  may  occur  indifferently  in  any  part. 

28.  Coenocytes. — Many  algse,  while  externally  like  others, 
which  are    divided   into  true   cells,    have  not   the  units   of 


LI X EAR   AND    SUPERFICIAL    AGGREGATES.       2$ 

structure  separated  by  cell-walls.  In  Vaucheria,  for  example, 
the  whole  of  the  vegetative  body  forms  a  single  chamber, 
in  which  lies  the  united  protoplasm,  corre- 
sponding to  many  cells,  as  shown  by  the 
numerous  nuclei  which  are  distributed  through 
it.  The  external  walls  of  the  cells  are  formed, 
but,  when  the  nuclei  divide  as  growth  proceeds, 
the  protoplasm  does  not  divide,  and  the  septa 
or  partition- walls  are  not  formed.  Such  an  un- 
septate  company  of  cells  is  called  a  ccenocyle. 

In  the  cladophoras  (fig.  29)  some  of  the 
normal  divisions  are  complete,  while  others 
are  only  nuclear  divisions.  Consequently  the 
cladophoras  seem  to  be  a  filament  of  true 
cells,  but  in  reality  each  apparent  cell  is  a 
ccenocyte,  as  shown  by  the  several  nuclei  in 
each  (fig.  30). 

29.  External  segmentation.  —  A  plant 
body  of  this  construction  may  attain  con- 
siderable size  and  complexity,  as  in  Caalerpa 
(fig.  31 )  and  Acetabularia  (fig.  32),*  even  to 
mimicking,  upon  a  small  scale,  the  form  of 
leafy  plants.  In  such  cases  the  external  walls 
become   considerably  thickened,    and   across  V,G    a9— a   single 

J  plant      of     Clado- 

the  protoplasm  and  its   large  vacuoles,  from    Mora,     showing 

profuse      monopo- 

one    side  of   the  chamber  to   the  other,    run     <iial    branching. 

Natural      size.    — 

irregular  bars  of  cellulose  which  act  as  braces     AfUr  Hauck. 
to  prevent  the  collapse  of  the  outer  walls  (fig.  ^^). 

In  Caulerpa,  particularly,  a  high  degree  of  development 
as  to  external  form  is  reached  (fig.  31  ).  There  is  a  stem- 
like axis,  v-s,  creeping  in  the  mud,  which  bears  green  leaf- 
like  branches,  b,  on  one  side  and  clusters  of  colorless  root- 


Note  carefully  the  scale  of  the  figures. 


24 


PLANT   LIFE. 


Fig.  31. 
Fig.  30.  — One  ccenocyte  from  a  branch  of   Cladophora,  shi 

chloroplasts  ;    /;,  pyrenoids ;    a,  starch-grains;    «,  nuclei. 

After  Strasburger. 
Fig.  31  — Part  of  a  plant  of  Caulerpa.      See  text,  r  29.      Two-thirds  natural  size. 

—After  Sachs. 


i-ing  fifteen  nuclei,     ch. 
Magnified  270  diam. — 


Fig.  32.  —  Acetabular ia.  A,  an  entire  plant,  natural  size  —After  Woronin.  A,  dia- 
grammatic longitudinal  sec  linn  through  the  upper  end  of  the  stalk  and  the  um- 
brella-like circle  of  crowded  branches  which  grow  together  ;  «,  scars  left  by  fall  of 
an  earlier  whorl  of  short  branches  ;  r,  w,  rudimentary  branches  ;  C,  the  base  of 
stalk  showing  rhizoids  for  attachment, _/",  and  for  storage,  b.  Magnified  20  diam. — 
After  De  Bary  and  Strasburger. 


LINEAR   AND    SUPERFICIAL    AGGREGATES.      2$ 


a    I  >ase 
shable, 


like    branches,    w,    on     the    other.       Not    only    are 

(posterior  end)  and   an  apex  (anterior  end)  distingu 

but  the  plant  shows  a  difference  between 

an  upper  (dorsal)  and   under  (ventral) 

side,  the  leaf-like  thallus  lobes  arising 

from    the    dorsal    side,    while    rhizoids 

spring  from  the  ventral  side. 

30.   The    thallus.  —  To    the    loose 

aggregation  Of  Single  Cells  into  Colonies  Fig.  33.  -  Transverse  section 

c    j     c     .         -  .,  ...  of  axis  of  Caulerpa,  show- 

Ot    definite   form,    as  well  as   tO   the  body       ing  cross-bars  to  stiffen  wall. 

r  lii-  •       ■  •  Magnified  about  25  diam. — 

formed  by  their  more  intimate  union  After  Murray. 
in  the  linear  and  superficial  aggregates  just  described,  the 
name  thallus  is  applied.  The  term  is  most  frequently  applied 
to  those  more  complicated  forms  which  constitute  the  vege- 
tative bodies  of  the  higher  algai,  which  are  now  to  be 
described. 


CHAPTER    III. 


THE   THALLUS    OF    THE    HIGHER   ALG^E. 


31.  From  linear  to  solid  aggregates. — From  the  fila- 
mentous algae,  whose  body  is  a  linear  aggregate  of  cells,  it  is 
but  a  step  to  those  forms  whose  body  is  a  superficial  aggre- 
gate. When  JMonostroma  grows  from  the  single  cell  as  which 
it  begins  life,  the  cell-divisions,  instead  of  occurring  succes- 
sively in  parallel  planes,  are  made  in  two  planes  at  right 
angles  to  each  other.  The  result  is  a  single  sheet  of  cells 
forming  a  leaf-like  thallus  attached  to  stones  or  other  algae. 
The  broader  forms  are  sometimes  20-25  cm-  whlc. 

Ulva,  a  near  relative,  develops  in  much  the  same  way, 
but  at  least  one  series  of  divisions  occurs  in  a  third  plane,  at 
right  angles  to  the  other  two,  so 
that  the  body  of  the  sea-lettuce  con- 
sists of  two  layers  of  cells.  As 
fig.  34  shows,  it  is  very  clearly  dif- 
ferentiated into  rhizoid  and  thallus. 
If  two  such  layers  separate  from 
each  other,  as  they  do  in  Entero- 
morpha,  a  hollow,  sac -like  body  is 
formed. 

So,  from  the  linear  aggregates, 
we  pass  through  superficial  to  solid 
aggregates  of  a  broadly  extended 
form. 

The  transition   from  linear  to  solid  aggregates  of  slender 

26 


Fig.  34. — A  small  plant  of  Ulva 
lactut  a.  the  sea  lettuce,  show- 
ing thallus,  and  rhiz..id  for 
attaching  it  to  rocks.  Natural 
size. — From  Bessey. 


THE    THALLUS   OF   THE   HIGHER   ALGSE.  2J 

form  may  be  understood  by  comparing  with  one  of  the  fila- 
mentous algas  a  member  of  an  isolated  order  of  green  fresh- 
water algre,  the  CharacecB. 

Characeae. 

32.  The  order. — These  plants  constitute  an  outlying  group 
of  considerable  antiquity,  having  no  near  relatives  living,  yet 
showing  in  the  vegetative  body  some  structural  resemblance 
to  the  filamentous  algre,  while,  as  a  whole,  their  external 
form  imitates  quite  closely  that  of  the  higher  plants  (figs. 
35,  36).  The  species  of  Chara  and  Nitella  (the  two  genera 
which  make  up  the  bulk  of  this  order)  are  found  in  almost 
every  temperate  region,  growing  in  dense  masses  submerged 
and  rooting  in  the  mud  in  quiet  waters.  They  reach  a  height 
of  10-75  cm- 

33.  External  form. — The  plants  agree  in  having  a  central 
axis,  at  certain  points  of  which  *  arise  lateral  outgrowths  of 
two  kinds.  One  kind  forms  a  circle  of  branches,  nearly  like 
the  main  axis,  except  that  their  growth  is  limited.  These 
themselves  bear  branches  of  simpler  structure.  The  primary 
whorled  branches  are  the  so-called  "  leaves,"  and  the  second- 
ary ones  which  these  bear  are  the  so-called  "  leaflets." 

Just  above  one  of  the  "leaves"  in  each  whorl  is  pro- 
duced a  branch  precisely  like  the  main  axis,  which  has,  like 
it,  unlimited  growth. 

34.  The  main  axis. — In  Nitella  the  axis  consists  of  alter- 
nately long  and  short  cells,  a  very  short  cell  occurring  at  each 
point  ("  node")  where  branching  occurs.  The  long  cell 
extends  from  one  "  node  "  to  another.      This   "  internodal" 

*  Commonly  called  nodes,  and  the  intervals  internodes.  These  terms, 
imposed  from  analogies  with  the  seed-plants,  are  entirely  misleading  from 
a  morphological  point  of  view,  as  are  also  the  names  "  leaves  "  and 
"  leaflets,"  applied  to  certain  divisions  of  the  axis,  hut  they  have  heroine 
so  fixed  that  it  is  difficult  to  avoid  their  use. 


28 


PLANT  LIFE. 


F,G-   35.— Upper  part   of  a   Dlani   .,{  ri  v. 

Krou-.h  (''leaves";,  and  a,  li;^,  1,1 '/''.' ;;;:;],s':'.w.l,1<  "honied  branches  of  limited 
lowest  being  cut  off.  The  small  |„  (|j, '  In  '  ™ncl,,'s.."f  unlimited  growth,  the 
organs.     Natural  sire  -After  wtle  C      'eaVes     are      ,eafl«* "  and  sex- 


THE    THALLUS   OF   THE  HIGHER   ALGM.         2Cj 

cell   is,  therefore,  of  an   extraordinary  length,  as  well  as  of 
large  diameter. 


Fig.  36. — Upper  part  of  a  plant  of  Nitella.     Natural 


30 


PLANT  LIFE. 


35.  Cortex. — Nitella  and  Chara  are  much  alike,  except 
that  in  Chara  the  main  axis  and  all  its  brandies  are  com  posed 
of  a  row  of  large  cells,  surrounded  by  a  jacket  of  smaller  ones 
(fig.  37).  The  walls  of  these  outer  cells  are  often  much 
thickened,  and  incrusted  with  salts  of  lime  to  such  an  cxtmt 
as  to  render  the  axis  very  brittle.  Around  the  main  axis  the 
cell-jacket  is  of  much  complexity  ;   it  becomes  more  simple 


■<>x 


Fig.  37. 


Fig.  38. 


Fig.  37.— Transverse  section  of  the  axis  of  Chara.  a,  internodal  cell;  b,  cortical  cells 
Magnified  about  30  diam.  —  From  a  drawing  by  C.  E.  Allen. 

Fig.  38.  —  Longitudinal  section  of  apex  of  axis  of  Chara.  x,  apical  cell.  The  seg- 
ment next  below  will  divide  into  a  nodal  and  an  internodal  cell  ;  the  next  one  has 
already  divided  and  the  nodal  half  has  again  divided  into  two  internal  and  several 
external  (only  •.;  show)  nodal  cells.  <-,  </,  internodal  cells  ;  between  them  a  node  pro- 
ducing the  branches  ("  leaves  ")  e  and/;  and  the  cortical  branches  a,  a.  6,  a  similar 
branch  growing  up  from  node  below,  only  its  tip  showing.  Magnilied  330  diam. — 
After  Sai  hs. 


upon  the  whorled  branches,  and  is  wanting  upon  the  ultimate 
divisions. 

While  a  cross-section  of  the  axis  shows  a  complete  union 
between  the  walls  of  the  cortical  cells  (b,  fig.  37)  and  the 
central  one  (a,  fig.  37),  a  study  of  their  development  shows 
that  they  are  originally  branches  of  the  outer  cells  at  each 
node,  which  likewise  produce  the  circle  of  "leaves."     The 


THE    THALLUS   OF   THE   HIGHER  ALGM.  31 

branches  from  the  node  above  grow  downward  and  others 
from  the  node  below  grow  upward  until  they  meet  and  inter- 
lock about  the  middle  of  the  internode  (fig.  38).  Thus,  the 
cortical  cells  are  not  produced  by  division  from  the  large 
central  cell  which  they  cover  and  stiffen,  but  simply  grow  over 
it  and  become  united  with  it  at  a  very  early  age,  increasing 
with  its  growth  and  undergoing  division  at  the  same  time,  so 
that  each  cortical  branch  becomes  multicellular. 

36.  Apical  cell. — The  axis  and  all  its  branches,  in  both 
genera,  are  produced  by  the  growth  of  a  single  apical  cell  of 
hemispherical  form  (x,  fig.  38).  The  segments,  successively 
cut  off  by  partition-walls  from  its  base,  each  divide  a  second 
time.  One  of  the  cells  so  produced  increases  rapidly  in  size, 
and  becomes  the  internodal  cell,  while  the  other,  by  succes- 
sive divisions  and  differentiation,  forms  the  node  and  its  ap- 
pendages. In  those  branches  which  show  unlimited  growth 
the  apical  cell  retains  its  hemispherical  form  until  death  ;  but 
in  the  divisions  with  limited  growth  ("leaves")  it  becomes 
pointed  and  ceases  to  cut  off  segments  from  the  base. 

37.  Rhizoids. — -The  structures  by  which  the  Characeos  are 
held  in  place  are  adapted  to  penetrate  the  soft  mud  of  the 
ponds  and  lakes  in  which  they  grow.  From  the  nodes  near 
the  base  of  the  axis  arise  numerous  colorless  rhizoids,  often 
of  considerable  strength  through  thickening  of  the  cell-walls. 

The  thallus  shows  decided  increase  in  specialization  of 
members.  This  is  accomplished,  however,  with  a  minimum 
of  differentiation  in  the  cells  of  which  the  body  is  composed. 

Polysiphonia. 

In  the  marine  alga?  a  still  higher  specialization  of  members 
is  reached.  One  of  the  red  seaweeds  may  be  used  to  show 
the  gradual  advance  in  complexity. 

38.  External  form. — The  body  oi Polysiphonia,  a  branch- 
ing alga   (fig.  39)  which  grows   in  abundance   upon   rocky 


32 


PLANT  LIFE. 


seacoasts,  is  not  divided  into  nodes  and  internodes,  and  the 
branches  are  differently  arranged  from  those  of  Chara.  The 
^  axis  is  made  up  in  its  larger  parts  of  five  or 

more  rows  of  cells,  the  central  or  axial  row 
being  surrounded  by  a  jacket  of  at  least  four 
>  others  (fig.  40).  But  these  originate  by 
f  i  division  from  the  central  one,  and  are  not,  as 
'  $  in  Chara,  merely  adherent  to  it.  It  is,  how- 
Yf       ever,  only  in  the  larger  parts  of  the  axis  that 


Fig 


Fig.  39.— An  entire  plant  of  Polysiphonia,  showing  mode   of  branching.     Natural 

size. — After  Kutzing.     (See  fig.  229.) 
Fig.  40. — Transverse  section  of  one  of  the  branches  of  Polysiphonia,  showing  a 

minute  central  cell  with  four  large  and  four  small  cells  surrounding  it.      Magnified 

about  50  diam. — From  a  drawing  by  Mr.  Grant  Smith. 
Fig.   41.  —  Apex  of  a  branch  of  Polysiphonia  which   has  nearly  ceased  growing. 

Magnified  about  100  diam. — From  a  drawing  by  Miss  Rowan. 

this  structure  appears  ;  at  the  tips  even  of  the  main  axis  the 
body  is  a  linear  aggregate  (fig.  41).  Polysiphonia,  there- 
fore, may  be  looked  upon  as  one  of  the  simplest  forms  of  a 
solid  aggregate. 

39.  Apical  cell. — As  in  Chara,  growth  in  length  is  quite 
definitely  localized,  because  it  is  the  elongated  terminal  cell 
of  either  the  main  or  secondary  axes  (fig.  41)  which  pro- 
duces, by  division  near  its  base,  the  new  cells  whose  subse- 
quent enlargement  and  division  give  rise  to  the  axis.  In 
some  red  algae  the  chambers  are  not  cells  but  ccenocytes,  as 
shown  by  the  several  nuclei. 

40.  Color. — -In  this  plant,  as  in  very  many  of  the  marine 


THE    THALLUS   OF   THE   HIGHER   ALGM. 


33 


alga;,  there  exists,  in  addition  to  the  green  of  the  chloro- 
plasts,  a  special  coloring  matter,  called  phycoerythrin.  To 
the  naked  eye,  this  color  overpowers  the  green  and  gives  the 


Fig.  42. — Upper  part  of  a  plant  of  Fucus  Tesieulosus.  r,  midrib  of  thallus  ;  /, 
bladders;  s,  swollen  tips  covered  by  numerous  elevations,  in  each  of  which  is  a  pit 
(conceptacle)   which    contains   many  sex-organs.     Two   thirds   natural   size. — After 

Luerssen. 

plant  a  pink  tinge.      In  other  red  algai  it  is  often  present   in 
greater  quantity  and  variety  of  hue,  so  that  brilliant  reds  and 


54 


PLANT  LIFE. 


purples,  with  shadings  of  brown  and  green,   mark  the  more 
striking  species. 

Fucus. 

From  the  very  simple  body  of  Polysiphonia  to  the  common 
bladder-wrack,  or  Fucus  vesiculosus,  there  are  all  stages  of 
complexity,  which  cannot  be  traced  here. 

41.  External  form. — The  body  of  Fucus  (fig.  42),  is 
large  as  compared  with  the  plants  previously  described.  It 
is  often   75-100  cm.   long  by  1-2    cm.   broad,  of  greenish  - 


Fig.  43. — A  transverse  section  of  the  thallus  of  Fucus,  showing  midrib,  r ;  cortex,  c  ; 
medulla,  m  ;  and  a  hair-pit,/.  Magnified  10  diam. — From  a  drawing  by  Mr.  C.  E. 
Allen. 

brown  color  and  cartilaginous  consistency.  Near  the  base 
the  thallus  is  contracted  into  a  stalk  whose  extremity  is 
broadened  into  a  sucker-like  disk  (often  lobed)  which  at- 
taches the  plant  firmly  to  the  wave- 
washed  rocks  on  which  it  grows. 
Above,  the  thallus  is  flattened,  with 
a  thicker  rib  in  the  middle  (fig. 
43),  and  branches  abundantly  by 
forking.  These  branches,  though 
often  twisted,  really  lie  in  the  same 
place  as  the  flattening.  Here  and 
there  the  axis  shows  pairs  of  oval 
f.g  44 -a  longitudinal  section  swellings,  the  bladders,  which,  by 
$Zl?£ent?lpST*l  the    contained   gases,  give  greater 

flattened  sides  oJebodyt/,ap,cal    buoyancy tQ   the  plants  in  the  Water. 

SWrfiSW&WE  42-  APical  cell.-An  examina- 
toiiii^ifiESdiSS!  tion  of  the  structure  of  the  thallus 
-After  Rostafinsk,.  shows  a  decided  differentiation  of 

cells,  which  would  be  expected  from  the  large  and  complex 


THE    THALLUS    OF    THE   HIGHER   ALG&.         35 

form.  At  the  apex  of  any  growing  branch  is  found  a  cluster 
of  angular  cells,  thin-walled,  of  nearly  uniform  size,  with 
abundant  protoplasmic  contents,  and  all  in  close  contact. 
( >ne  of  these  cells,  lying  in  the  center  of  the  group,  some- 
what larger  and  of  different  shape  from  the  rest  {c,  fig. 
44),  is  constantly  undergoing  division,  and  thus  cutting  off 
cells  (segments)  from  its  two  inner  faces  (1,  2,  3,  fig.  44). 
The  cells  so  produced  undergo  further  divisions,  forming 
thereby  all  the  cells  of  which  the  thallus  is  composed.  This 
group  of  dividing  cells  is  present  in  all  the  higher  plants. 
It  constitutes  the  "  growing  point  "  or,  better,  the  apical  (or 
primary)  merislem.  The  single  cell  from  which  all  proceed 
in  Fucus  is  called  the  initial,  or  apical,  cell. 

43.   Differentiation  of  cells. — But  if  a  thin  section  of  the 
thallus,  from  an  older  part,  be  examined  (fig.  45),  its    cells 
will   be  found  very  different  from  those 
at  the  apex.      The  cells  nearer  the  sur- 
face  are  smaller  and  of  different  form 
from   those   in   the    interior.      They  are 
also  close-set,  whereas  those  in  the  in- 
terior are  no  longer  in  contact  with  each 
other  on  all  sides,  but  have  been   sep-       **=>  ^5^^^> 
aratec    l>v  the  ^rowim:  oi   branches  from        ^.i,,/.,*^.  ■..-»•  «••«  ■• 

J  .    ?.  ,  ffe      ,.        rp,         ummmmm 

the  cortical  cells  between  them.       1  hese 

Fi<;.  45—  Diagram  of  a  por- 

filamentous  branches  are  crossed  and  in-      tion  of  fig.  44,  magnified 

about  70  clum     1    cortex: 

terlaced,  with  wide  intercellular  spaces,      w,  medulla.   Thevaried 

forms  of  the  cells  are  due 

All  of  these  older  cells  have  enlarged,      to  the  different  planes  in 

.  .  which   the  filaments  are 

and,   instead  Ol    being  Idled  With    protO-       cut.   The  clear  spaces  are 

filled  with  mucilage  pro- 

plasm,  they  will  be  found  to  have   large     duced  by  the  ceff-waiis. 

From    a   drawing  by  Mr. 

vacuoles     and    heterogeneous    contents.      C.  E.  Allen. 
The   walls,  also,  are  no  longer  thin   and   homogeneous,  but 
have  become  thickened  and  differentiated   into  at  least  two 
layers,  the  outer  of  which  is  capable  of  swelling  enormously 
in  water,  while  the  inner  layer  retains  its  usual  form.      There 


36 


PLANT   LITE. 


arises  thus  a  cortex,  as  the  outer  dense  part  is  called,  and  a 
medulla  or  pith,  as  the  mucilaginous  and  apparently  isolated 
central  cells  and  filaments  are  called.  At  the  bladders,  the 
pith  becomes  filled  with  air  and  other  gases. 

44.  Special  functions. — Complete  examination  of  all  parts, 
the  disk  of  attachment,  the  bladders,  and  the  hair-pits  (fig. 


Fig.  46. — Several  plants  of  Lessonia,  showing  tree-like  thallus  and  branched  rhizoids 
attaching  the  plants  to  rocks,     jB  natural  size.—  After  I  .<•  Maout  &  Decaisne. 

43)  with  which  many  species  are  covered,  would  reveal  still 
other  modes  of  differentiation  of  cells  from  those  of  the 
apical  meristem.  Accompanying  the  change  of  form  is 
always  specialization  of  function,  which  we  can  interpret 
only  in  a  very  imperfect  fashion   from  our  own  standpoint. 


THE    THALLUS   OF    THE   HIGHER   ALGJE. 


37 


The  compact  small  cells  forming  the  surface  are  nutritive 
and  probably  in  part  protective  ;  the  bladders  serve  to  in- 
crease the  buoyancy  of  the  plants  when  the  tide  is  in  ;  while 
the  abundant  mucilage,  formed  in  the  interior  from  the  cell- 
walls,  serves  to  retain  the  moisture  when  the  plants  are  ex- 


showing  differentiation  of  thallus.     Natural  size. — 
After  !■<  nnett  >v  Murray. 

posed  by  the  ebbing  tide  ;  the  hair-pits  are  functionless,  so 
far  as  known  ;  and  the  strong,  elastic  cells  of  the  disk  and 
stalk  above  hold  the  plants  in  place  as  they  sway  constantly 
back  and  forth  in  every  wave  of  the  rising  or  falling  tide. 

45.    Color. — The   coloring    matter   in   the   chloroplasts   of 
Fucus  and  other  brown  seaweeds   is  chlorophyll  (green)  and 


3$  PLANT-  LIFE. 

phycophoein  (brown).  The  chloroplasts  exist  chiefly  in  the 
cortex,  which  is,  therefore,  the  food-making  tissue  (see  ■"  230), 
while  the  internal  tissues  are  used  for  storage  of  reserve  food. 

46.  Intercalary  zones  of  growth. — Some  of  the  brown 
seaweeds,  instead  of  growing  at  the  tip,  grow  in  a  zone  at 
the  base  of  the  flatter  part  of  the  thallus,  just  above  the  round 
stalk.  Such  growth  is  called  intercalary  growth.  There  can 
be  no  single  initial  cell,  but  at  least  a  zone  of  initials. 

Some  species  grow  to  great  lengths.  One  Australian  species 
is  said  to  attain  a  length  of  200-300  meters.  Still  others 
have  the  form  of  a  tree,  the  stalk-like  portion  representing 
the  trunk,  with  a  crown  of  flattened,  frond-like  branches 
above  (fig.  46). 

The  thallus  in  the  "gulf-weed,"  or  " sea-grape  "*  (fig. 
47),  is  still  further  differentiated  into  rounded,  stem-like  parts 
and  flattened,  leaf-like  ones.  The  bladders  are  berry-like 
enlargements  in  the  middle  of  short,  rounded  branches,  and 
the  form  is  strikingly  like  that  of  a  small  herb. 

*  This  plant  is  of  interest,  also,  because  from  its  scientific  name,  Sar- 
gassum,  is  derived  the  name  of  that  region  in  the  North  Atlantic,  in  the 
loop  of  the  Gulf  Stream,  the  Sargasso  Sea,  where  the  plants  accumulate 
after  being  torn  off  the  tropical  shores  on  which  various  species  grow. 


CHAPTER    IV. 

THE  FUNGUS  BODY  OF  HYPHAL  ELEMENTS. 

Fungi. 

Fungi  are  plants  without  chlorophyll,  whose  body  is  gen- 
erally made  up  of  long  filaments,  either  loosely  or  densely 
interwoven  and  united. 

47.  Origin. — As  the  bacteria,  the  smallest  and  simplest 
plants,  were  derived  from  the  lowest  algae  by  slow  adaptation 
to  a  different  kind  of  food,  so,  at  various  points  in  the 
ascending  scale  of  algal  life,  certain  algae  have  adapted  them- 
selves to  the  use  of  organic  food  which  they  could  secure 
ready-made.  These,  having  no  use  for  the  chlorophyll  and 
chloroplasts,  have  gradually  lost  them.  The  adoption  of  the 
habit  has  proved  highly  successful,  both  among  the  simple 
bacteria  and  the  more  highly  organized  true  fungi.  The 
ancestors  of  the  present  species  were — how  long  ago  no  one 
can  say — probably  at  first  chiefly,  if  not  exclusively,  aquatic. 
Some,  at  the  present  time,  have  the  same  habit,  growing  in 
infusions  of  organic  matter.  Others  attach  themselves  to  dead 
or  even  living  animals  or  plants  in  the  water.  The  soil  (con- 
taining in  its  upper  layers  more  or  less  organic  matter  from 
the  offal  of  plants  and  animals,  or  from  their  dead  bodies) 
and  dead  or  living  organisms  furnish  places  of  growth  for  a 
great  number  of  species  which  have  adapted  themselves  to 
other  than  aquatic  life. 

48.  Hyphae.— The  filaments  of  which   the  fungus  body   is 

39 


40  PLANT  LIFE. 

composed  are  called  hyphne.  Each  is  the  result  of  growth 
from  a  single  cell,  and  is  comparable  to  the  thread-like  body 
of  the  filamentous  algae. 

There  is,  naturally,  a  great  variety  in  the  hyphas  of  differ- 
ent species  of  fungi.  Some  are  relatively  large  ;  others  very 
small ;  some  of  even  diameter  and  caliber,  others  irregular 
and  with  unequally  thickened  walls  ;  some  very  thin-walled, 
others  very  thick -walled.  Between  these  extremes  is  to  be 
found  a  complete  gradation. 

They  grow  in  length  at  the  apex  only.  In  many  kinds 
partitions  are  formed  at  more  or  less  regular  intervals,  as  the 
growth  in  length  proceeds.  In  others  no  partition-walls  are 
formed,  though  division  of  the  nucleus  takes  place.  Even 
when  transverse  partitions  are  formed,  they  do  not  separate 
the  filaments  into  cells,  but  each  chamber,  or  sometimes  the 
whole  filament,  is  a  coenocyte. 

49.  Branching. — As  the  hyphos  elongate,  branching  may 
occur.  If  a  branch  is  to  be  formed,  a  limited  area  of  the  cell- 
wall  begins  to  grow  more  rapidly  than  the  rest.  This  allows 
a  slight  bulging  of  the  growing  region; 
the  swelling  increases  and  soon  takes 
the  form  of  a  branch,  like  the  main 
axis.  It  may  remain  short  or  continue 
to  grow  indefinitely  in  length.  Com- 
monly a  septum  is  formed  at  the  base 
of  the  branch.  If  such  a  branch  arises 
first  as  a  minute  pimple,  so  that  it 
remains  connected  with  the  parent  axis 

Beer-yeast(Sacc/taro-  . 

cerevisi.r).   «,  a  full-  by  a  small  neck,  and  has  only  limited 

crown    plant    with    a   branch  ... 

'lhii(l)  partially  developed.    /',  growth     111     length,     it     IS    Called    a    blld 

r,  colonies  formed  by  budding, 

the  individuals  still  attached,  and  the  process  is  known  as  budding 

Magnified  750  diam.-Aftcr   ,.  ox         e      ,     .  ,  ,, 

Reess.  (fig.  48).     Such  branches  are  usually 

easily  broken  off,  thus  readily  producing  independent  plants. 
(See  further  under  Reproduction,  *  302.)     In  some  species  of 


THE   FUNGUS  BODY   OF  HYPHAL   ELEMENTS.     41 

fungi,  profuse  branching  is  the  rule;  in  others,  the  branches 
are  few. 

50.  Mycelium. — When  branching  is  profuse,  or  when  a 
considerable  number  of  individuals  grow  near  together,  the 
filaments  often  become  interwoven  and  entangled  in  so  com- 


Fic.  4g.— A  single  plant  of  Mucor  Mucedo,  showing   the   mycelium  as  it  developed 
from  a  single  spore  in  an  infusion  of  dung.     It  bears  a  single  erect  reproductive 

branch  rising  above  the  fluid.      Magnified  .•■■,  diam.      Afler  Urcteld. 


plex  a  web  that  it  is  impossible  to  follow  a  single  hypha  for 
any  distance.  Such  a  mat  of  hyphse  is  called  a  mycelium, 
a  term  which  is  also  used  to  designate  the  vegetative  hypha? 
collectively,  whether  forming  a  felted  mass  or  not  (figs.  49, 
50).     The  mycelium  may  be  formed  wholly  upon  the  sur- 


42 


PLANT  LIFE. 


face  of  the  object  upon  which  t  he  fungus  lives;  or  parts  of 
it  may  be  superficial,  and  part  may  penetrate  that  object ;  or 
all  of  it  may  be  hidden  within  the  substratum.*  In  some  of 
the  common  molds  (Mucorini),  the  cobwebby  threads  lying 
upon  the  surface  of  the  substratum  constitute  the  exposed 
part  of  the  mycelium,  while  other  hyphae   penetrate  deeper  ; 

K 


Fig.  50. — A  section  of  part  of  the  aerial  body  of  Polyporus.  s/>,  hyphae  running  at  an 
angle  to  the  section,  cut  across  ;  A",  crystals  of  oxalate  of  lime.  Magnified  about 
500  diam.      Attn   Vogl. 

in  others  (Penicillium,  etc.),  the  superficial  hypha?  become 
so  interwoven  that  they  may  be  lifted  off  the  substratum  (as 
from  jellies,  jams,  syrups,  etc.)  as  a  coherent  layer.  But  in 
most  cases,  especially  when  the  fungus  grows  on  a  solid 
medium,  the  hyphae  become  adherent  to  it  and  permeate  it 
SO  that  they  cannot  be  separated  from  it,  even  by  the  most 
careful  dissection. 

*  This  non-committal  term  may  be  used  to  designate  the  material  upon 
which  the  vegetative  part  of  the  fungus  grows,  whether  it  be  a  living 
body,  a  dead  organism,  or  organic  matter  in  solid  or  liquid  form. 


THE   FUNGUS  BODY   OF  HYPHAL    ELEMENTS.      43 

51.  Parasites. — Especially  is  this  true  of  those  fungi  which 
grow  in  the  interior  of  living  organisms.  The  higher  plants 
are  liable  to  be  fastened  upon  by  parasitic  fungi,  and  com- 
pel led  to  act  as  hosts  to  their  unbidden  and  unwelcome  guests. 
Such  a  host  plant  may  be  entered  when  a  mere  seedling,  in 
which  case  the  fungus  grows  with  its  growth,  or  it  may  not 
be  attacked  until  older  or  even  mature.  The  host  may  be 
permeated  in  all  its  parts  by  the  fungus  filaments  ;  or  certain 
members,  only,   such  as   the   leaves,   flower   parts   or  twigs, 


Fig.  51.—  Young  hyphae  of  Exobasidium  developing  from  spores,  .?/,  entering  the 
air-pores  of  the  leaf  of  the  cranberry.  Others,  from  .</',  j/",  penetrate  the  skin 
directly.     Magnified  about  600  diam  — After  Woronin, 

may  be  affected.  The  effect  of  the  fungus  upon  the  host  is 
often  scarcely  visible  to  the  unaided  eye;  sometimes  a 
local  disturbance  is  manifested  by  swelling,  unnatural  color 
or  growth;*  sometimes  the  affected  members  become  dis- 
torted and  useless  or  are  even  killed  ;  sometimes  the  disease 
is  general  and  is  followed,  slowly  or  quickly,  by  general 
death  of  the  host. 

52.  Infection. — These  internal  parasites  obtain  entrance 

*  Sec  further  ""'   222,  464. 


44 


PLANT  LIFE. 


to  their  hosts  in  various  ways.  Sometimes  the  young  hypha, 
growing  from  a  special  reproductive  body  (spore),*  so  minute 
that  it  may  easily  float  in  the  air  and  fall  upon  a  leaf,  creeps 
along  the  surface  till  it  finds  one  of  the 
microscopic  openings  in  the  skin  of  the 
leaf,  into  which  it  grows  (sp,  fig.  51). 
These  external  openings  are  connected 
with  irregular  spaces  between  most  of 
the  cells  of  the  softer  parts,  which  are 
also  the  parts  in  which  the  food-supply 
s  most  abundant.  In  these,  therefore, 
the  fungus  develops,  breaking  out  to 
the  surface  again  to  form  or  set  free  its 
reproductive  bodies. 

Or,  the  young  hyphae  may  excrete 
at  their  tips  a  substance  which  so  soft- 
ens or  dissolves  the  cell-walls  of  the 
host  that  they  penetrate  these  cells 
readily,  not  only  at  the  surface  (sp' , 
sp" ,  fig.  51),  but  in  the  interior. f  They 
then  branch  freely,  often  growing  in 
the  spaces  between  the  cells,  often 
passing    through    the    cells    themselves 

Fig.    52— Hyphae    of     Fra-  l  h  ° 

metes  Pitii  perforating  the  ({\^t     C2). 
walls  of  a  wood-cell  (at  c)  ol  v    °'    3    /' 

Scotch  pine  and  destroying      Plants  are  often  attacked  when  mere 

the  primary  wall  ol  the  cell. 

d .'.holes  made  by  hypha.  seedlings.      Either  from   a  bit  of  my- 

Magnified  about  800  diam.  °  ' 

—After  r.  Hanig.  celium  or  a  spore  which    has  survived 

the  winter  or  the  dry  season,  a  hypha  grows,  which,  almost 
as  soon  as  the  seedling  emerges  from  the  seed,  penetrates  it. 
The  fungus,  in  these  cases,  may  develop  quickly  and  kill  the 


*  See  II  304  and  the  following. 

f  It  is  not  improbable  that  the  penetration  of  cell-walls  is  assisted  by 
such  pressure  as  the  growing  hypha  can  exert,  hut  the  relative  action  of 
enzymes  and  pressure  has  not  been  determined. 


THE  FUNGUS  BODY  OF  HYPHAL   ELEMENTS.     45 

young  plant  (as  in  the  "damping  off"  disease  in  green- 
houses), or  it  may  develop  slowly  and  not  reach  maturity 
until  the  host  is  mature. 

53.  Haustoria. — Those  fungi  which  grow  upon  the  sur- 
faces of  living  plants  (and  those  which  grow  in  the  internal 
air-spaces)  often  have  special  branches  for  fastening  them- 
selves to  the  host  or  absorbing  food  from  it.      In  the  surface 


Fig.  53. — Epidermis  and  a  few  cortical  cells  of  cowberry  with  mycelium  of  Calyp- 
tos/>ora  occupying  the  intercellular  spaces  and  pressing  knob-like  ends  against  the 
cells  from  which  a  slender  branch  penetrates  the  wall  and  enlarges  i 


into  sac-like  haustoria,   b,  b.     a,  club-shaped  hyphae  which  produce  spore-mother- 
cells,  c\  in  the  epidermis.     Magnified  420  diam.— After  K.  Hartig. 

fungi  these  are  usually  very  short,  disk-like  or  lobed 
branches  which  do  not  penetrate  the  cells  of  the  host.  In 
other  cases  they  are  branches  of  minute  diameter,  which 
enter  the  cells,  and  either  enlarge  into  a  knob  (fig.  53)  or 
branch  profusely  (fig.  54). 

54.  Fusion. — When  the  hyphre  of  a  fungus  grow  very 
close  together,  they  frequently  cohere  and  become  so 
changed  in  appearance  as  to  lose  all  trace  of  resemblance  to 
filaments.       Not    only  fusion    but    thickening    and    division 


46 


PLANT  LIFE. 


occur,  and  a  section  of  the  resulting  structure  has  much  the 
appearance  of  a  section  of  the  tissues  of  ;i  higher  plant  (fig. 
55).  These  changes  arc  particularly  apt  to  occur  among  the 
superficial  parts  of  the  more  massive  structures  among  the 
fungi,  where  they  are  necessary  to  impart  firmness,  rigidity, 
or  durability.  For  example  :  in  the  ergot,  a  fungus  common 
upon  certain  grasses,  a  portion  of  the  mycelium  is  to  survive 
the  winter  and  grow  again  the   next   season.      This  portion 


Fig.  54.  Fig.  5-.. 

Fig.  54. — Branching  haustoria  of  Peronospora.  m,  m,  the  hypha  traversing  an 
intercellular  space  of  the  host;  g,  z,  two  haustoria  penetrating  two  tills  of 
the  host  and  branching  therein.  The  other  contents  of  host-cells  not  shown. 
Magnified  about  400  diam. — After  De  Bary. 

Fig.  55. — A  section  through  the  mycelium  of  a  lichen  showing  hypha;  near  upper  sur- 
face, a,  and  lower  surface,  6,  fused  into  a  false  tissue  ;  only  in  central  region  are  tin- 
filaments  recognizable.  The  dark  spheres  are  imprisoned  alga;.  Magnified  650  diam. 
— After  Bornet. 

replaces  the  young  ovulary  of  the  flower  (see  1"  335),  and, 
as  it  matures,  becomes  a  dark-colored  mass,  as  firm  and  re- 
sistant as  the  grain  itself  (fig.  56). 

The  interweaving  and  fusion  of  the  hypha?  sometimes  pro- 
duce cord-like  or  strap-like  structures  of  considerable  size.. 
The   mycelia  of  the  higher  fungi  frequently  form  them,  and 


THE  FUNGUS  BODY   OF  HYPHAL   ELEMENTS.     A7 


they  may  be  found  in  the  leaf-mold  of  forests   or  in  rotten 
stumps  or  between  boards  in  wet  places. 


Fig.  56.— a,  compact  mycelium  of  ergot  in  the  form  of  a  grain-like  body,  replacing 
grain  of  rye  ;  l>,  the  same  germinating  to  form  reproductive  bodies.  Natural  size.— 
After  Tulasne. 

54a.  Lichens. — The  body  of  lichens  is  a  mycelium  woven 
about     isolated    unicellular    algae,     colonies,    or    filaments, 


48  PLANT   LIFE. 

which  are  thus  imprisoned.*  The  fungus  hyphae  usually  pre- 
dominate and  in  great  measure  determine  the  form  of  the 
body  and  its  texture.  Sometimes  the  algae  are  present  in 
such  numbers  that  the  hyphae  seem  merely  distributed  among 
them.  In  form  the  body  may  be  broad  and  thin  (fig.  225), 
or  slender  and  shrub-like.  In  texture  it  may  be  tough  and 
leathery,  with  the  hyphae  near  the  surface  fused  into  a  false 
tissue  (a,  b,  fig.  55).  When  gelatinous  algae,  such  as  Nostoc 
(see  •'  13)  are  imprisoned,  the  body  may  be  gelatinous. 
In  all  cases  the  algae  supply  the  fungus  with  food,  and  are  in 
turn  supplied  with  water  absorbed  by  the  spongy  mycelium. 
(See  further  \\  195,  223,  462.) 

*  Rarely  about  other  small  green  plants. 


CHAPTER   V. 

LIVERWORTS  AND   MOSSES. 

55.  Alternation  of  generations. — In  the  liverworts  and 
mosses,  as  in  all  the  plants  higher  in  the  scale,  there  occur 
two  well-marked  phases  in  the  course  of  their  lives.  One  of 
these  phases  is  marked  by  the  formation  of  sexual  reproduc- 
tive cells,  or  gametes  (see  *H  369),  the  egg  and  sperm, 
whence  it  is  called  the  sexual  phase,  or  the  gametophyte .  The 
other  is  characterized  by  the  formation  of  non-sexual  repro- 
ductive cells,  the  spores  (see  "[  304),  whence  it  is  called  the 
non-sexual  phase,  or  sporophyte.  These  two  phases  alternate 
with  each  other,  the  sexual  reproductive  cells  of  the  game- 
tophyte producing,  under  suitable  conditions,  the  sporophyte, 
whose  non-sexual  reproductive  cells  give  rise  to  the  game- 
tophyte. To  this  regular  sequence  of  the  two  phases  the 
phrase  alternation  of  generations  has  been  applied.* 

In  the  higher  liverworts  and  mosses  both  phases  have 
nutritive  work  to  do,  but  in  many  this  is  confined  to  the 
gametophyte,  and  in  all  the  gametophyte  carries  on  the 
greater  part  of  it.  To  this  phase,  therefore,  attention  is 
first  given. 

Liverworts. 

56.  The  thallus. — The  form  and  structure  of  the  vegeta- 
tive body  of  the  simplest  liverworts  is  scarcely  different  from 

*  Rather  obscure  suggestions  of  the  alternation  of  generations  are  to  be 
found  among  the  alg;e  and  fungi,  tint  they  are  not  definite  enough  to 
warrant  discussion  in  this  book.  Let  the  student  notice,  however,  that 
this  feature  does  not  appear  suddenly  in  plant  life,  though  introduced 
abruptly  into  the  account  of  it. 

49 


50 


PLANT  LIFE. 


that  of  some  of  the  green  algae.     The  body  is  a  thallus  with 
rhizoids  (fig.  57).    The  rhizoids  are  usually  linear  aggregates 


Fig.  57. — A,  plants  of  Riccia  sorocarpa,  on  the  ground.  Gametophyte  phase.  Nat- 
ural size.  B,  a  vertical  section  of  one  of  the  thick  lobes  of  the  thallus,  showing 
nearly  uniform  structure.  The  thallus  has  nearly  covered  over  two  young  sporo- 
phytes  which  appear  as  though  in  the  interior.  Rhizoids  arise  from  the  ventral  side 
and  flanks.     Magnified  about  25  diam. — After  I5ischoff. 


of  cells  having  thin  walls  and  little  protoplasm,  arising  from 
the  under  side  and  flanks  of  the  thallus.      They  serve  to 


Fig  58.— Portion  of  a  vertical  section  of  the  thallus  of  Lunularia  cruciata.  a, 
dorsal,  i,  ventral  epidermis;  c,  an  air-pore;  <•,  air-chamber,  from  whose  floor  rise 
cell-rilainrnis,  ,/ ;  _/,  partition  between  adjoining  air-chambers;  g;  colorless  cells 
containing  starch,  some  showing  net-like  thickenings  of  the  walls,  others  with  oil- 
bodies,  //;   1,  a  ventral  scale  ;  /,  a  rhizoid.     Magnified  110  diam. — After  Nestler. 


fasten  the  thallus   to  the  substratum, — an  adaptation  to  the 
terrestrial    mode    of  life.      The    thallus   is  usually    fiat   and 


LIVERWORTS  AND    MOSSES. 


expanded  in  a  horizontal  plane,  though  sometimes  much 
crisped.  The  simpler  ones  consist  of  several  layers  of  uniform 
cells*  (£,  fig.  57). 

57.  The  dorsiventral  thallus. — In  other  forms  there  is  a 
more  decided  difference  between  the  upper  and  under  sides 
of  the  thallus.  The  upper  cells  contain  chloroplasts, 
while  the  under  ones  have  none  or  very  few.  In  the  Mar- 
chantia  family  there  are  large  air-chambers  in  the  upper  part 
of  the  thallus,  from  the  floor  of  which  arise  filaments  or 
cactus-like  rows  of  chlorophyll-bearing  cells  (fig.  58).  On 
the  under  side,  also,  are  frequently  found  scale-like  out- 
growths (superficial  aggregates),  as  in  fig.  58,  i. 

A  part  which  shows  constant 
differences  between  an  upper  (dor- 
sal) and  an  under  (ventral)  side  is 
said  to  be  dorsiventral,  and  the 
state  of  being  thus  different  is 
termed  dorsiventrality. 

58.  Branching. — The  branching 
of  the  thallus  is  always  by  forking, 
in  a  single  plane  or  direction,  as  in 
Fucus,  but  the  branches  do  not 
always  develop  equally.  Some- 
times special  branches,  instead  of 
remaining  horizontal,  grow  upright 
and  develop  into  peculiar  forms 
adapted  to  producing  the  sexual 
reproductive  organs  (fig.  59). 

59.  The  growing  point  of  the  thallus  is  usually  in  a  notch 
at  the  apex  (fig.  60).  There  is  a  single  apical  cell  of  wedge 
shape  (rarely  tetrahedral),  from  whose  inner  faces  segments 
are    cut    off  (fig.    61).       These,    by    division    and    growth, 


oung,  one  mature),  f<  >r 
g  sex-organs.  Nal  ui  tl 
\ti,r  Bischoff. 


*Ccenocytes  rarely    appear    in    the   vegetative    bodies  of  this   or    any 
higher  group. 


52 


PLANT  LIFE. 


produce  the  whole  thallus.  The  center  of  the  thallus  is 
generally  thicker  than  the  wings,  and  forms  a  sort  of  central 
rib  (B,  fig.  60). 

60.    The  shoot. — In   the  greater  number  of  liverworts  the 
mature  vegetative  body  is  a  shoot,  which  is  differentiated 


Fig.  60. 


Fig.  61. 


Fig.  60.— Surface  view  of  growing  apex  of  thallus  of  Metzgeria  furcata  just  after 
forking,  a,  primary  apical  cell;  />,  secondary  apical  cell  of  branch;  c,  the  wing- 
tissue  between  axis  and  branch  outgrowing  the  apices.  B,  the  midrib.  Magnified 
160  diam.— After  Kny. 

Fig.  61. — Diagram  showing  origin  of  branch  in  Metzgeria  furcata.  a,  primary 
apical  cell  from  which  the  segments  right  and  left  bounded  by  heavy  lines  have 
been  cutoff.  All  have  undergone  further  division.  In  the  right-hand  one  the  latest 
cell-walls  have  been  so  placed  as  to  form  a  wedge-shaped  cell,  />,  which  becomes 
the  apical  cell  of  a  branch.  Its  early  formation  gives  the  (false)  appearance  of 
dichotomy. — After  Kny. 


into  stem  and  leaves  (figs.  62,  63).  Even  in  such  a  body 
the  dorsiventral  character  is  well  marked.  The  stem  is  a 
filiform  axis  of  uniform  cells,  bearing  three  (rarely  more  or 
fewer)  rows  of  leaves,  of  which  the  two  dorsal  rows 
are  the  larger,  while  the  under  leaves  are  much  smaller,  even 
to  being  inconspicuous  or  wanting.  These  leaves  are  super- 
ficial aggregates,  consisting  of  uniform  cells  richly  supplied 
with  chloroplasts,  as  are  also  the  outer  cells  of  the  stem. 
Their  form  is  very  varied  and  often  of  great  beauty.  They 
are  always  sessile  and  are  usually  crowded  so  closely  as  to 
overlap  each  other  more  or  less,  and  hide  the  axis  com- 
pletely (fig.  63). 


LIVERWORTS   AND    MOSSES. 


53 


61.  The  origin  of  the  leaves  will  be  apparent  upon  com- 
paring figures  64,  65,  and  66.  In  Blasia  (fig.  64)  the  thallus 
is  lobed,  i.e.,  the  edge  has  not  grown  equally,  but  continued 
growing  longer  at  certain 
points.  In  Fossombronia  ( fig. 
65)  the  flattened  thalloid 
form  is  still  evident,  but  the 
lobing    has  become   so    deep 


€> 


Fig    62. 


Fig.  63. 


Fig.  62.— Gametophyte  of  Hazztniiti  XoTce-Hollandite.  Besides  the  ordinary- 
branches  there  are  slender  ones  (flagella)  with  sparse  minute  leaves.  Naturalsize. 
— After  Lindenberg  and  Gottsche. 

Fig.  63.— A,  dorsal  view;  A',  ventral  view  of  a  piece  of  fig.  6a,  magnified  about  12 
diam.,  showing  the  stem,  bearing  two  dorsal  rows  of  large  leaves  and  one  ventral 
row  of  small  ones.— After  I.indenberg  and  Gottsche. 

that  the  almost  separate  parts  are  usually  called  leaves. 
In  Noteroclada  (fig.  66)  the  central  axis  is  still  more  com- 
pact, and  has  lost  its  flat  form,  becoming  a  rounded  stem 
from  whose  flanks  arise  regular  outgrowths,  the  leaves,  each 
of  which  corresponds  to  one  of  the  lobes  of  the  thallus  in  the 
other  forms. 

Mosses. 

In  the  mosses  the  complexity  of  the  mature  vegetative  body 
is  somewhat  greater.  It  is  always  developed  as  a  shoot  differ- 
entiated into  stem  and  leaves. 

62.    Rhizoids. —  The   shoot  is  anchored,  as   in  the  liver- 


54 


PLANT  LIFE. 


Fig.  64 


Fig.  64.— Part   of  a   plant   of    Blasia  pusilla.     The  flattened  lobed  thallus  is  the 

gametophyte;  the  stalked  capsules  (one  young:,  one   bursted)  are  two  sporophytes 

attached  to  it.     Magnified  4  diam. — Alter  Schiffner. 
Fig.  65. — Gametophyte  and  sporophyte  of  Fossombronia  cristata.     The  thallus  is 

so  deeply  lobed  thai  the  divisions  are  usually  called  leaves.     Magnified  15  diam.— 

After  Schiffner. 


Fig.  66.— A,  a  gametophyte  of  Noteroclada,  with  a  sporophyte  attached.  Natural 
size.  B,  a  part  of  the  stem  and  a  single  leaf  of  the  same,  magnified  about  10  diam. 
— After  Hooker. 


LIVERWORTS   AND    MOSSES. 


55 


worts,  by  numerous  usually  much  branched  rhizoids  (A,  fig. 
67;  iv,  fig.  68).  Similar  filaments  may  be  produced,  often 
in  great  numbers,  along  the  stem  and  especially  in  the  axils 
of  the  leaves,  or  they  may  even  arise  from  the  leaves  them- 
selves, when  the  plants  grow  in  dense  patches  or  in  a  very 
moist  place. 


Fig.  67.—.-/,  gametophyte  of  Polytrickum  commune,  with  rhizoids  below.  /?, 
gametophyte  of  Hylocomium  splendens,  bearing  three  sporophytes  near  top. 
Natural  size.  — After  Kerner. 

63.  The  stem  is  usually  cylindrical  and  covered  by  the 
crowded  leaves.  In  structure  it  generally  shows  an  advance 
upon  that  of  the  liverworts  in  having  the  whole  of  the  outer 
region  occupied  by  a  distinct  mass  of  mechanical  tissue  com- 
posed of  thick-walled  cells,  and,  near  the  (enter,  a  strand  of 
elongated  small  cells,  known  as  "conducting  tissue"  (fig. 
68),  though  it  is  doubtful  whether  it  conducts  anything. 


56 


PLANT   LIFE. 


Fig.  68. — Transverse  section  of  the  stem  of  Bryum  roseum.  In  the  center  the 
small  cells  make  a  central  strand,  the  "conducting  tissue  ";  the  surface  cells  form 
an  epidermis;  the  next  three  rows  within  also  have  thick  walls  an. 1  strengthen  the 
stem;  w,  rhizoids  arising  from  epidermis.     Magnified  50  diam. — After  Sachs. 


Fig.  69. 

Fig.  69.— A,  leaf  of  a  moss  [Funaria  Americana),  showing  central  rib.  Magnified 
about  40  diam.;  />',  upper  portion  of  the  same  leaf,  highly  magnified,  showing 
single  layer  of  cells  forming  the  blade  and  the  narrower  cells  of  the  thick  rib.— 
After  Sullivant. 

Fig.  70  —Tip  of  leaf  of  a  moss  (Oligotrickum  aligerum\  showing  the  thickened 
rib,  and  the  plate  like  ridges  on  blade  and  rib  greatly  increasing  the  surface  of 
nutritive  tissue.     Magnified  about  75  diam. —  After  Sullivant. 


L 1 1  ~ER  IVOR  TS    A  iVD    MOSSES. 


57 


64.  The  leaves  arc  also  more  highly  developed  than  in 
liverworts.  They  are  always  sessiie  and  are  arranged  in  two 
(rarely),  three,  or  more  vertical  ranks  along  the  stem,  and 
consist  usually  of  a  single  sheet  of  chlorophyll-bearing  cells, 
the  blade  (figs.  69,  70),  and  a  central  rib  running  from  base 
to  apex  (frequently  wanting),  which  is  composed  of  elongated 
conducting  and  strengthening  cells  (figs.  69,  70).  In  some 
the  amount  of  green  tissue  is  increased  by  the  formation  of 
vertical  plates  similar  to  the  blade  (fig.  70). 

65.  Branching.— The  stem  branches,  often  very  profusely, 
by  the  formation  of  lateral  growing 
points  beneath  the  developing  leaves. 
Sometimes  the  growth  of  the  lateral 
branches,  as  of  the  original  main 
axis,  is  checked  by  the  formation 
of  sexual  organs.  In  that  case  a 
new  branch  is  likely  to  arise  some 
distance  below  the  apex,  so  that  the 
stem  is  a  succession  of  lateral 
branches,  called  a  sympodium  (fig. 
71).  This  mode  of  branching  is 
termed  sympodial.  In  other  cases 
the  main  axis  continues  its  growth 
unchecked,  and  more  or  fewer 
branches  also  develop.  These  lie 
plainly  upon  the  sides  of  a  central 
axis.  This  mode  of  branching  is 
called  monopodia!.  Often  the 
growth  of  the  lateral  axes  is  defi- 
nitely limited  and  their  develop- 
ment regular,  forming  a  pinnate 
branch-system.  If  the  secondary 
axes  themselves  branch,  there  is 
even  tripinnate  system,  as  in  figure  67,  B. 


Fig.  71.  Axis  of  a  moss  (Ortho- 
trie It  u  m)  showing  sympodial 
branching.  .V,  5»,  .V3,  • 
ii\  e  1  lusters  "I  sexual  organs, 
produced  at  apex  which  check 
the  growth  "I  axis.  Beneath 
each  a  lateral  growing  point 
develops,  produi 

the  brances  /•'.  /•''.  6*.  Magni- 
fy d  n  >li. mi.  Alter  Bruch  & 
Scbimper. 

formed    a    bi pinnate    or 


58 


PLANT  LIFE. 


66.  Protonema.  —  In  its  early  stages  the  vegetative  body 
of  the  hafv  liverworts  and  the  mosses  is  either  a  flat  thallus, 
similar  to  the  mature  form  of  the  thallose  liverworts,  or  a 
branching  filamentous  body,  called  the  protonema,  almost 
identical  with  the  form  of  the  filamentous  algae.  Upon  this 
protonema  the  leafy  shoot  arises  as  a  lateral  bud,  which  soon 
outstrips  it  in  growth  and  differentiates  leaves.  The  proto- 
nema may  live  for  some  months,  but  generally  perishes  after 
having  produced  a  few  lealy  plants. 

67.  Sporophyte. — The  non-sexual  phase  in  the  liverworts 
and  mosses  has  almost  no  vegetative  functions,  and  a  fuller 


Fig.  72. — A,  two  capsules  of  Rryum  ;  from  the  right-hand  one  the  lid  1ms  fallen, 
showing  the  teeth.  Magnified  5  diam  />',  four  gametophyte  shoots  of  Splachnunt 
ampullaceum,  bearing  four  sporophytes.  Natural  size.  C,  a  capsule  "I  one  <>f 
the  same  sporophytes,  showing  enlarged  apophysis,  a,  below  the  sporangium,  j. 
Magnified  10  diam.  />.  capsule  of  Splachnum  luteum,  with  umbrella-like  apo- 
physis, a,  below  sporangium,  .v      Magnified  2  diam. 

study  of  its  structure  is  left  for  Part  III.  It  consists  at 
maturity  of  a  yellowish  or  brown  spherical  or  cylindrical  case 
(fig.  72),  which  is  sessile  or  raised  upon  a  short  or  long 
stalk  and  contains  (a  iew  or)  hundreds  or  thousands  of 
reproductive  cells  called  spores.  The  base  of  this  stalk 
constitutes  an  organ  called  the  "foot,"  which  is  embedded 
in  the  gametophyte  (_/",  fig.  73). 

68.  Nutrition. — The  surface  of  the  young  sporophyte, 
when  large  and  well  developed,  as  it  is  in  the  higher  liver- 
worts and  mosses,  is  green.  To  a  limited  extent,  therefore, 
it    is  able   to   make    food  ;  but   not   sufficient   for  its  needs, 


LIVERWORTS   AND    MOSSES. 


59 


for  these  arc  great  on  account  of  its  rapid   growth  and  the 
supply   required    as    reserve    for 

each  spore.  The  foot,  being  in 
close  contact  with  the  tissue  of 
the  gametophyte,  acts  as  an 
absorbing  organ,  receiving  food 
solutions  from  it.  The  sporo- 
phyte  thus  lives,  in  part  at  least, 
as  a  parasite  upon  the  gameto- 
phyte. 

In  some  mosses  there  is  a  ten- 
dency to  increase  the  nutritive 
work  of  the  sporophyte  by  de- 
veloping at  the  top  of  the  stalk, 
below  the  spore-case,  a  mass  of 
green  tissue.  InBryumfyi,  fig. 
72)  this  gives  the  capsule  a  pear- 
shape,  while  in  Splachnum  {B, 
C,  D,  fig.  72)  it  is  so  far  de- 
veloped as  to  exceed  the  spo- 
rangium. In  some  species  it  is 
expanded  into  a  miniature  um- 
brella which,  one  can  imagine, 
might  readily  become  segmented 
into  leaves. 

The  intimate  attachment  of  sporophyte  to  gametophyte 
continues  throughout  the  life  of  the  former.  Sometimes  the 
gametophyte  perishes  at  the  close  of  the  growing  season,  but 
more  commonly  it  is  perennial,  growing  and  branching  at  the 
anterior  end  as  the  older  posterior  parts  die  away. 


Fig.  73.— Yonni;  sporophyte  of  Phas- 
i urn  cuspidatum.  c,  columella ;  f, 
foot,  embedded  in  gametophyte  stem; 
s,  seta  (cells  not  shown);  s/>s,  spo- 
rangium ;  s/>,  spore-mother-cells. 
Magnified  80  diara.— After  Kienitz- 
Ge*rloff. 


CHAPTER   VI. 

FERNWORTS  AND  SEED-PLANTS. 

Fernworts. 

Among  the  still  more  complex  plants,  the  ferns  and  their 
allies,  the  same  "alternation  of  generations"  can  be  seen. 
The  two  "generations,"  or  phases,  have,  however,  changed 
much  in  relative  size.  Whereas  in  the  liverworts  and  mosses 
the  gametophyte  is  much  the  larger  and  more  conspicuous,  as 
well  as  the  longer-lived,  among  fernworts  the  sexual  phase  is 
so  much  smaller  that  it  is  seldom  seen ;  and  in  some  species 
it  is  almost  microscopic.  On  the  other  hand,  the  sporophyte 
is  the  phase  which  is  usually  seen  and  the  only  part  popularly 
known. 

69.  The  gametophyte. — The  vegetative  body  of  this  phase 
of  the  fernworts  in  its  best  developed  forms 
is  a  small, flattened,  green  body  of  oblong, 
orbicular,  or  cordate  outline,  commonly 
less  than  half  a  centimeter  in  diameter, 
rarely  as  much  as  2  cm.  (fig.  74).  It  is 
strikingly  like  a  thallose  liverwort  in 
general  form,  being  distinctly  dorsiventral 
and    having   rhizoids    on    its  under  side, 

Fig.  74.  —  Ventral  side  of  .  ,  . 

the  gametophyte  of  a  which  fasten  it  in  place.     (  because  of  this 

lem.Asplenium.    The     ,       ,    .  .     .  .     ,  .  , 

notched  end  is  the  an-  thallOld    form    and    because    it    seemed    to 
tenor.     Rhizoids    near  ,  ,  .        .  ,,  , 

posterior emi.  Tin  small  precede     the    "real    plant     — a    popular 

circles  show  position  of      ,  .  , 

male  organs ;  the chim- phrase    meaning    the    sporophyte — it   was 

ney-like  projections  near        ,,     ,  ,i     n-         \       i-\    -\         \  .1 

anterior  end  the  female   Called     A    />nt///tl///l/W .)         Only     the     Central 

diam.    After  k r.      part  01   the  gametophyte  consists  of  more 

than   one   layer  of  cells.      On  the  under  side  of  this  central 

60 


J- /.A. VIVO  NTS   AND    SEED-PLANTS. 


61 


"cushion,"  as  it  is  called,  are  produced  the  sexual  organs. 
(See  further  under  Reproduction,  Tart  III.) 

70.   Reduction  of  gametophyte. — In  a  few  of  the  fernworts 
the  gametophyte  is  filamentous,  or  tuberous,  and  more  or  less 


N 


Fig.  75.  —  Sporophyte  of  a  fern,  Polypodiu 
stem,  hearing  seenndary  roots  and 


ilgare,  showing  horizontal  underground 
■s.     Natural  size. —  From  Bessey. 


completely  subterranean  and  colorless.     Such  prothallia  derive 
tluir  food  from  decaying  plant-offal. 

In  higher  plants  of  this  group  the  gametophyte  becomes 
still  further  reduced  in  size  and  structurally  simplified,  until 
in  some  species  it  is  hardly  more  than  a  few  cells  surrounding 
the  sexual  organs.      These  reduced  forms  grow  by  the  use  of 


62 


PLAN T   LIFE. 


food  stored  in  the  spore  from  which  they  originate.  The 
gametophyte  of  such  species  has  lost  wholly  its  vegetative 
character,  and  is  restricted  in  function  to  the  production  of 
the  sexual  organs. 

71.    The  sporophyte. — In  contrast  with  the  smallness  and 
simplicity  of  the  gametophyte  is  the  relatively  large  size  and 


Fig.  76.— Embryo  of  Pteris  aguilina,  and  a  small  part  of  the  gametophyte,  gy  in 
which  its  foot,/,  is  embedded,  r,  the  primary  root  ;  s.  primary  stem  ;  /,  primary 
leaf.  Induced  growth  of  the  gametophyte  about  the  foot  is  shown  by  small  size  and 
numbei  of  cells.     Much  magnified. — After  Hofmeister. 


Fig.  77  — Section  through  embryo  and  gametophyte  of  maidenhaii  fern  (AdiantutH 
Capillus-Veneris).  The  embryo  is  older  than  that  in  tig.  76.  /,/,  gametophyte; 
A,  rhizoids,  among  which  are  two  spermaries.  The  eggs  in  three  ovaries  failed  to 
develop  ;  the  other  formed  the  embryo,  E.  a,  primary  stem,  only  slightly  de- 
veloped (compare  s,  fig.  76)  ;  b,  primary  leaf  ;  iu,  primary  mot.  The  part  embedded 
in  the  fjametophyte  is  the  foot.     Magnified  about  10  diam.     After  Sachs. 

complexity  of  the  sporophyte  (fig.  75).  It  is  always  differ- 
entiated into  stem  and  leaves,  and,  with  rare  exceptions, 
roots  also.  This  great  advance  in  the  development  of  the 
sporophyte  of  the  fernworts,  as  contrasted  with  its  form  in 
their  nearest  of  kin  below,  the  liverworts  and  mosses,  suggests 
that  the  fernworts  are  a  very  old  group  ;  a  hint  which  is  con- 
firmed by  the  antiquity  of  their  fossil  remains.  It  is  also 
noteworthy  that,  as  compared  with  mossworts,  the  chief  work 


FEXA'irORTS   AND    SEED-PLANTS. 


63 


of  nutrition  has  been  shifted  from  the  gametophyte  to  the 
sporophyte  j  and  this  even  when  the  gametophyte  has  its 
largest  size  and  greatest  duration,  while  nutritive  work  is 
wholly  abandoned  in  the  smaller  forms.  The  sporophyte  has 
also  become  the  long-lived  stage,  the  gametophyte  being 
usually  transitory  (only  exceptionally  living  more  than  one 
season),  while  the  sporophyte  lives  through  one  season  in  the 
few  annuals,  and  commonly  for  several  or  even  many  years. 

72.  The  embryo. — The  fertilized  egg,  from  which  the 
sporophyte  arises,  develops  while  still  embedded  in  the 
gametophyte  in  which  it  is  formed.  Consequently  the 
embryo  sporophyte  is,  as  in  the  mossworts,  at  first  surrounded 
by  the  gametophyte  (figs.  76, 
77).  The  part  of  the  gamet- 
ophyte adjacent  to  the  embryo 
grows  under  the  stimulus  of  its 
presence,  but  the  growth  of  the 
embryo  is  more  rapid,  and  it 
consequently  spreads  apart  the 
gametophyte  (see  figs.  76,  77). 
A  portion  of  the  embryo  de- 
velops a  temporary  organ,  the 
foot,  which  remains  embedded 
in  the  gametophyte  until  the 
first  root,  stem,  and  leaf  have 
been  formed  (fig.  78).  Soon 
thereafter  the  gametophyte  per- 
ishes and  the  foot,  no  longer 
useful,  disappears. 

73.  Members. —  The  mature 
sporophyte  is  differentiated  into 
root,  stem,  and  leaves.  The 
important  adaptations  of  the 
structure  and-forms  of  these  members  are  so  similar  to  those 


Fig.  78 


same   as   fiff.    77 


The  gametophyte,  /\  seen  from  be- 
low, w  11  li  1  In.-. lids  ;  the  sporophyte 
•-nil  attached  Inn  with  primal  \  leaf",  .'. 
developed  into  blade  and  stalk  ;  /.  the 
primary  root:  .-.  .1  secondary  runt, 
arising  from  tin-  juncture  oi 
and  st<-iii  Magnified  about  4  diam. 
After  Sachs. 


64  PLANT  LIFE. 

of  the  seed-plants  that  thay  will  be  discussed  in  connection 
with  them. 

Seed-plants. 

Among  the  highest  plants,  those  which  produce  seeds,  the 
differentiation  of  the  body  is  essentially  the  same.  The 
alternation  of  sexual  and  non-sexual  phases  is  still  traceable, 
though  greatly  obscured  by  the  extreme  reduction  of  the 
gametophyte.  This  tendency  to  the  reduction  of  the  sexual 
phase,  which  was  remarked  in  passing  from  the  mossworts  to 
the  fernworts,  continues,  until  in  the  highest  seed-plants  the 
gametophyte  is  wholly  microscopic.  Even  by  the  aid  of  the 
microscope,  it  is  possible  to  identify  only  the  sexual  organs 
which  it  produces,  and  one  or  more  cells  which  are,  perhaps, 
the  rudiments  of  its  vegetative  body.  The  sporophyte,  con- 
sequently, is  the  only  phase  of  the  seed-plant  visible  to  the 
unaided  eye.  The  relation  of  the  gametophyte  to  it  will  be 
explained  in  Part  III. 

The  body  of  the  sporophyte  exhibits  the  same  members, 
viz.,  stem,  root,  and  leaf,  having  the  same  general  form,  and 
subject  to  the  same  modifications,  as  in  the  fernworts.  To  a 
discussion  of  the  vegetative  members  of  the  fernworts  and 
seed-plants  we  now  turn. 


CHAPTER   VII. 

THE   ROOT. 

74.  Analogous  members. — It  has  been  pointed  out  that, 
among  the  lower  plants,  there  are  very  many  which  possess 
structures  similar  in  form  and  function  to  the  root,  and 
sometimes  called  by  the  same  name.  Although  these  parts 
serve  to  hold  the  plant  in  place,  and  perhaps  to  absorb 
material  from  the  substratum,  they  are  not  to  be  looked  upon 
as  homologous  with  the  roots  of  the  higher  plants,  but  as 
merely  analogous  with  them.  In  the  plants  whose  vegetative 
body  is  a  thallus  the  gametophyte  is  the  prominent  phase. 
In  no  case  does  the  gametophyte  produce  true  roots.  It  is 
not  until  the  sporophyte  becomes  an  independent  plant  that 
true  roots  are  found  in  the  vegetable  kingdom.  It  is,  there- 
fore, only  among  fernworts  and  seed-plants  that  these  organs 
are  to  be  found.  When  the  sporophyte  is  developed  as  an 
independent  plant,  it  becomes  necessary  for  it  to  produce 
some  organ  capable  of  holding  it  in  place,  or  of  absorbing 
materials  from  the  outside,  or  of  doing  both.  The  organ 
developed  to  meet  this  need  is  the  root. 

75.  Primary  roots  — In  accordance  with  their  origin, 
roots  are  either  primary  or  secondary.  Primary  roots  are 
those  which  are  developed  directly  from  the  egg  from  which 
the  entire  plant  takes  its  rise.  The  spherical  egg  in  most 
of  the  fernworts  begins  its  development  by  a  division  into 
hemispheres.  The  hemispheres  divide  into  quadrants  ;  ea<  h 
of  the  quadrant  cells  divides  into  two,  forming  octants  of  the 
original  egg.  Division  continues  and  the  fundaments  of 
primary  root,    foot,   stem,  and  one   or    more    leaves   appear 

65 


66 


PLANT   LIFE. 


(see  fig.  76).  In  many  of  the  seed-plants  the  egg  divides 
several  times  in  parallel  planes,  forming  a 
short  filament,  the  suspensor  (figs.  79-82). 
The  terminal  cell  of  this  row  may  then 
give  rise  to  an  embryo,  as  just  described, 
or  this  terminal  cell  and  an  adjacent  one 
may  take  part  in  forming  the  embryo.  In 
this  case  the  terminal  cell,  by  its  divisions, 
either  produces  the  primary  leaf  or  leaves, 
t  produces  the  primary  stem  and 
r,  s,  ceils  of  the  suspen-  leaves  ;   while  the  second  cell  gives  rise  to 

sor;  a,  a,  fi,  cells  from  ° 

:1V  H.Khiyr^: the  Primary  stem  and  root>  or  to  the 

fied. -Afur  Sachs.        primary  root  alone  (see  figs.  80-82). 
The    two  primary    members  formed 
from  the  root   hemisphere  of  fernworts 
are  not  always  permanent.     The  foot  is 


Fig.  79.— A    very   young   or 

embryo   of    the   onion. 


Fig.  80.  Fig.  81.  Fig.  82. 

Fig.  80.— A  very  young  embryo  of  shepherd's-purse.    Suspensor,  s,  s.  just  completed, 

and  first  four  cells  of  embryo  formed   by  division  of  terminal  one  ;  the  sei  ond  1  ell, 

/>,  is  to  produce  part  oi  the  root.     Highly  magnified. — After  Hanstein 
Fig.  81.  — An   older   stage  of  the   same.      /.',  embryo;  /•',  /■".  two  cells   resulting  from 

division  of  b.  fig.  80;  *.  s.  suspensor.     The  shaded    cells    produce    the   skin   and   the 

vascular  bundles      Highly  magnified.— After  Hanstein. 
Fig.  82.— An  older  embryo  of  same.      £,  embryo;  /.   /,  primary  leaves;   .9/.  apex  of 

stem  ;    r,  primary  root  ;  re,  first  layer  of  root-cap;  .r,  suspensor.      Cells  shown  only 

in  part.     Less  magnified  than  preceding.-    \fter  Hanstein. 


THE   ROOT.  67 

always  temporary,  disappearing  as  the  embryo  becomes 
larger.  It  is  sometimes  wanting  from  the  first.  In  both 
femworts  and  seed-plants  the  primary  root  is  rarely  wanting, 
but  often  short-lived,  dying  after  the  plant  has  established 
itself  and  has  formed  secondary  roots  to  take  its  place.  In 
many  cases,  however,  the  primary  root  persists  throughout 
the  life  of  the  plant. 

76.  Secondary  roots. — Secondary  roots,  on  the  contrary, 
are  those  which  arise  upon  stem  or  leaf,  or  even  upon  the 
primary  root  itself.  In  the  last  case  they  are  distinguished 
from  branches  of  the  primary  root,  which  arise  in  regular 
succession  toward  the  apex,  by  originating  out  of  this  regular 
order.  Secondary  roots  are  also  called  adventitious  roots. 
They  may  take  their  origin  at  any  point  upon  any  of  the 
members.  Their  point  of  origin  will  depend  largely  upon 
external  conditions.  They  are  especially  likely  to  be  formed 
upon  those  parts  which  are  in  contact  with  the  substratum, 
or  from  those  parts  which  are  kept  moist.  Upon  stems  they 
are  most  apt  to  appear  near  the  nodes.  (See  1  119.)  If 
the  plant  as  a  whole  is  surrounded  by  very  moist  air,  roots 
may  appear  at  any  point  of  the  surface.  Secondary  roots 
arising  thus  upon  a  part  of  the  plant  exposed  to  the  air,  and 
growing  for  all  or  part  of  their  existence  in  the  air,  are  also 
called  aerial  roots.  Familiar  examples  are  to  be  seen  about 
the  lower  part  of  the  stem  of  Indian  corn,  the  English  ivy, 
the  poison-oak,  the  trunks  of  palms  and  tree-ferns.  Secon- 
dary roots  often  arise  in  regular  succession  toward  the  grow- 
ing apex  of  the  stem,  particularly  in  plants  which  have  creep- 
ing or  subterranean  stems. 

77.  Growing  point.  —  Primary  and  secondary  roots  do 
not  differ  materially  in  their  structure.  The  early  divisions 
of  the  quadrant  cell  which  produces  the  primary  root  in  tern- 
worts  are  so  arranged  that  a  cell  shaped  like  a  four-sided 
pyramid    is    produced.      This    cell    becomes    the    apical,    or 


68 


rLANT  LIFE. 


initial,  cell.  It  is  situated  with  one  face  directed  toward  the 
apex  of  the  root  (see  fig.  83),  and  the  other  three  faces 
within  it.  Parallel  to  the  three  inner  faces  partitions  are 
constantly  formed  in  regular  succession  dividing  this  apical 
cell  into  two  unequal  portions,  so  that  the  smaller  is  looked 
upon  as  a  segment  cut  off  from  the  larger  portion.  If  these 
inner  faces  be  numbered  respectively  1,  2,  3,  the  segments 
are  constantly  produced  in  the 
order  of  the  numbers.  These 
segments  themselves  divide  to 
form  other  cells,  and  thus  give 
rise  to  all  the  tissues  of  the  root. 
This  mass  of  actively  dividing 
cells  is  the  primary  meristem  or 
growing  point  of  the  root  (com- 
pare •  101).  As  the  older  cells 
of  the  primary  meristem  enlarge, 
divide,  and  differentiate,  they 
are  constantly  pushing  the  apical 
cell  further  away  from  the  older 
part.  Not  only' are  segments 
cut  from  the  three  inner  faces  of 
the  apical  cell,  but,  at  less  fre- 
through  the  extremity  of  a  root  of   quent  intervals,  partitions  paral- 

Marsiha.       1  he   larjic  triangular  cell       1  »    '  I 

near  center  of    figure   is  the  apical     le|    t0    tne    outer  face  fQrm    sjmj_ 

cell.      I  lie   segments  from  the  inner 

faces  may  be  readily  traced  back-    pu  segments.       The    division  of 

ward;  thus  the  dotted  line  e<    points  ° 

to  the  fourths  to  the  sixth    segment      tnese     sc<rmentS     oiveS     HSe     tO     3. 
from  the  posterior  n.nht-hand  tare  "1  °  ° 

apicaiceii.   e/>,  root -caP  (epiderm.s);   strUcture  covering  the  very  tip 

ec.  cortex;  c,  stele;  en,  endodermis  o  •         1 

(pan  .,f  cortex^;  fie ,  peri.  v.  i.  (part   0f  the  root,  and  connected  with 

of  stele).    Magnified  about  ioo  diam. 
After  Van  Tieghem.  it  for  a  short  distance   only.       It 

receives,  therefore,  the  appropriate  name  of  root-cap  {ep,  fig. 

83).      Since  the  cells  of  the  surface  of  the  root-cap  are  older 

and  firmer  than  the  inner  segments  and  the  initial  cell,  and 

lie  in  front  of  them,  they  serve  to  protect  the  more  delicate 


Fig.  83.— Medial,  longitudinal   section 


THE    ROOT. 


69 


cells  as  the  growth   of  those  behind  constantly  pushes  the 
apex  forward  through  the  soil. 

In  seed-plants,  the  segments  of  the  egg  which  produce  the 


^v 


Fig.  84.  Transverse  section  of  a  young  root  (frown  in  soil,  showing  root-hairs  with 
adherent  soil-partii  les,  the  cortex,  and  the  stele.  Magnified  about  20  diam.— After 
Frank. 

root  do  not  divide  so  as  to  form  a  single  apical  cell,  but  a 
group  of  initial  cells,  which  retain  tin-  power  of  rapid  division 
and  constitute  a  primary  meristem  or  growing  point.  In  all 
other  respects  the  development  of  the  root  from  this  group 
of  initials  is  similar  to  that  already  described. 


7° 


PLANT  LIFE. 


In  both  cases,  the  differentiation  of  cells  produced  at  the 
growing  point  results  in  the  formation  of  three  characteristic 
parts  of  the  root,  namely,  (i)  an  outer  layer  or  layers,  the 
epidermis  ;  (2)  an  inner  region,  the  stele  ;  (3)  between  these, 
the  cortex. 

78.  1.  The  epidermis  usually  becomes  many-layered. 
At  the  apex  it  constitutes  the  root-cap  (ep,  fig.  83).  On  the 
other  parts  of  the  root  it  sometimes  sloughs 
off  entirely,  exposing  the  cells  of  the  cortex 
itself,  as  in  the  monocotyledons  (lilies, 
grasses,  sedges,  etc.);  or,  more  commonly, 
only  the  outer  layer  sloughs  off,  leaving  the 
innermost  as  the  covering  of  the  cortex. 

79.  (a)  Root-hairs. —  Those  cells  which 
form  the  surface  of  the  root, 
whether  they  be  the  origina 
epidermis  or  cortical  ones 
which  have  been  exposed 
by  its  loss,  usually  develop 
a  large  number  of  hairs, 
known  as  root-hairs  (fig. 
84).  These  root-hairs  are 
branches  of  the  superficial 
cells  (  fig.  85),  and  maybe 
looked  upon  as  simple  ex- 
tensions of  them,  as  the 
finger  of  a  glove  is  the 
extension  of  its  palm.  Only 
one  root-hair  arises  from  a 
superficial  cell.  They  arc 
usually  unbranched  and  without  transverse  partitions.  Only 
in  rare  cases  are  they  wanting.  They  live  for  a  shorter 
or  longer  time,  but  are  always,  as  compared  with  the 
duration  of  the  root,  quite  transient.      The  older  part  of  the 


Kig.  85. — Two  root-hairs  showing  structure 
and  relation  to  superficial  cells  of  root; 
grown  in  water  and  therefore  not  distorted 
as  in  fiji.  84.  A,  the  younger ;  />',  older, 
nearly  mature.  n,  nucleus  embedded  in 
cytoplasm;  vacuole  single  and  very  large. 
Highly  magnified.— After  Frank. 


THE   ROOT.  71 

root,  therefore,  is  without  root-hairs  because  of  their  death. 
The  youngest  part  of  the  root  is  likewise  free  from  them, 
because  they  have  not  yet  been  produced.  As  the  root  grows 
in  length,  new  root-hairs  are  continually  being  produced  and 
the  older  ones  are  dying  at  an  equal  rate,  so  that  a  zone 
of  hairs  is  found  only  upon  the  younger  parts  of  the  roots. 

80.  (/>)  The  root-cap,  serving  to  protect  the  tenderer  por- 
tion of  the  root  behind,  is  itself  constantly  exposed  to  injury. 
The  outer  and  older  cells  of  the  root-cap  are,  therefore,  either 
torn  away  through  mechanical  contact,  having  become  gradu- 
ally loosened  from  each  other  with  age;  or,  losing  their 
active  contents,  they  degenerate  and  break  down  into  a 
slightly  mucilaginous  material  which  facilitates  the  passage  of 
the  root  through  the  substratum.  This  degeneration  or  the 
mechanical  wear  is  repaired  constantly  by  the  formation  of 
new  cells  in  the  growing  point.  The  thickness  of  the  root- 
cap,  therefore,  is  maintained  throughout  its  existence  without 
considerable  change.  It  rarely  becomes  more  than  a  few  cell- 
layers  thick.  Since  its  tissue  is  produced  only  by  the  division 
of  the  apical  cell  or  cells,  it  is  organically  connected  with  the 
root  only  at  the  very  tip;  but  it  usually  extends  backward  over 
the  root,  by  reason  of  its  growth,  for  a  considerable  distance. 
If  the  finger  be  supposed  to  represent  the  root,  a  short  finger- 
stall, if  it  were  attached  to  the  tip  of  the  finger,  might  be 
fairly  taken  to  represent  the  position  of  the  root-cap.  Only 
in  rare  cases  is  the  root -cap  entirely  wanting. 

81.  2.  The  stele. — Occupying  the  center  of  the  root,  and 
surrounded  on  all  sides  by  the  cortex,  is  an  aggregate  of 
tissues  called  the  central  cylinder,  or  stele  (figs.  84,  86,  89). 
The  outermost  layer  of  its  cells  is  the  peru  vele  (figs.  86,  88, 
89).  Within  this  are  found  strands  of  elongated  cells  or 
cell-fusions,*   called    vascular    bundles,    or    strands.     These 

*  These  are  continuous  chambers  formed  by  the  breaking  down  of  the 
partition  walls  between  the  abutting  ends  of  cells.  They  are  usually 
devoid  of  living  contents. 


72 


PLANT   LIFE. 


bundles  are  of  two  kinds,  xylem  bundles  and  phloem  bundles, 
so  placed  that  they  alternate  with  each  other  about  the 
periphery  of  the  stele  (figs.  86,  88,  89).  The  xylem  bundles 
may  be  in  contact  with  one  another  in  the  center,  or  the 
center  of  the  stele  may  be  occupied  by  a  pith  (figs.  86,  89). 


Fig.  86. — Transverse  section  of  the  stele  and  a  portion  of  the  surrounding  cortex  of  the 
root  of  calamus,  j,  .v,  innermost  layer  of  cortex,  the  endodermis,  adjoining  outermost 
layer  of  stele,  the  pericycle;  /.  xylem  bundles;  ph,  phloem  bundles.  The  shaded  ele- 
ments of  xylem  bundles  are  the  primary  xylem  ;  the  large  ones,  g,  are  secondary.  In 
the  center  of  the  stele  and  between  the  bundles  is  conjunctive  tissue.  Highly  magnified. 
— After  Sa<  lis. 

The  tissues  of  the  xylem  are  usually  lignified  (see  ^[  9) 
and,  when  abundant,  make  up  what  is  called  the  wood.  They 
are  the  chief  water-conducting  elements  of  the  older  parts  of 
the  root. 

The  tissues  of  the  phloem  are  usually  not  lignified,  and  the 
most  important  ones  are  the  sieve-lubes,  which  conduct  proteids 
from  above  to  the  growing  regions  of  the  root. 


THE   ROOT.  73 

The  number  of  vascular  strands  constituting  the  stele  is 
various,  being  as  few  as  four  or  as  many  as  forty.  The 
ordinary  number,  however,  is  from  eight  to  twenty.  (See 
figs.  86,  89.) 

82.  3.  The  cortex  generally  consists  of  large  thin-walled 
cells  which  have  become  partially  separated  from  each  other, 
leaving  larger  or  smaller  intercellular  spaces  (figs.  86,  89). 
Its  innermost  layer,  bordering  the  stele,  is  usually  quite 
different  from  the  rest,  and  is  recognizable  by  its  wavy,  radial 
walls,  which  are  suberized  (^[  9).  This  layer  is  called  the 
endodermis  (figs.  86,  88,  89). 

83.  Duration. — Even  when  the  primary  root  persists 
throughout  the  entire  life  of  the  plant  secondary  roots  often 
appear.  When  the  primary  root  perishes,  its  functions  must 
be  performed  wholly  by  secondary  roots,  which  are  developed 
in  succession  upon  those  parts  where  they  are  useful.  The 
secondary  roots  themselves  may  be  either  permanent  or  tran- 
sient. In  creeping  plants  particularly,  whether  growing  on 
land  or  in  water,  the  functions  of  the  root  are  likely  to  be 
handed  on  to  successively  younger  roots,  the  old  ones  perish- 
ing and  dropping  off.  If  the  roots  endure  for  a  considerable 
time,  they  may  retain  their  primitive  structure  and  form,  or 
they  may  undergo  secondary  changes  which  unfit  them  for 
absorbing  organs,  and  adapt  them  to  subserve  various  special 
functions. 

84.  Secondary  changes. — Shortly  after  any  portion  of  the 
root  has  ceased  to  increase  in  length,  and,  therefore,  within 
the  first  season,  it  ordinarily  undergoes  minor  secondary 
changes  which  may  or  may  not  be  followed  by  more  profound 
alterations.  These  changes  affect  its  primary  structure  in 
various  ways  and  to  various  degrees  according  to  the  parts 
concerned. 

85.  1.  External  secondary  changes. — In  some  cases  the 
older  roots  differ  from  the  younger  in  scan  civ  more  than  the 


74 


PLANT  LIFE. 


loss  of  the  external  layer  of  cells,  from  which  the  root- 
hairs  arose.  The  sloughing  off  of  this  layer  of  cells  carries 
with  it  the  hairs  themselves  and  exposes  the  next  inner  layer 
of  cells,  which  had  before  become  slightly  altered  so  as  to  be 
rather  impervious  to  water.  Upon  their  exposure,  this  altera- 
tion proceeds  further,  so  that  they  become  almost  or  quite 
incapable  of  being  penetrated  by  the  soil-water  to  which  they 
may  be  exposed.  It  follows  from  this  that  it  is  only  the 
younger  part  of  the  root,  that  is,  the  portion  which  has  not 
undergone  secondary  changes,  which  is  capable  of  absorbing 
water.  In  many  roots  this  is  the  only  change  which  occurs. 
In  a  greater  number  certain  tissues  become  thick-walled,  so 
that  the  root  is  also  strengthened. 

In  a  few  instances,  the  root-cap  is  cast  off  from  the  tip. 
This,  however,  only  occurs  when  the  growth  in  length  of  the 
root  is  permanently  stopped. 

86.  2.  Internal  secondary  changes. — In  a  large  number 
of  roots,  especially  those 
\  'of  dicotyledons  and  gym- 
'1  nosperms,  the  secondary 
changes  result  in  increasing 
the  diameter,  sometimes 
very  greatly.  Increase  in 
diameter  comes  about  by 
the  formation  of  concentric 
layers  of  new  tissue  in  two 
or  more  regions.     The  new 


J©" 


o 


Fig.  87. — Transverse  section  of  the  periphery  of     ,    11  ,      _j„__j    ■        u 

the  root  ol  Clusia,  showing  the  formation  of  Cells   aie  piodliced   111    each 

periderm,     ec,  cells  of  cortex:  ap,  the  super-  .:_._     l         .  1,                         »: 

ncial  cells  of  the  root  (suberized);   per,  the  region    by    tile     resumption 

periderm,  its  inner  cells  (opposite  per)  actively  ,-       ,•          1      •        ,     •          1 

&yidmgbytangentialwalls,itstw,M,ute.l.v.rs.  ot  active  division  111  a  layer 

//'.snheri/.id.  its  innermost  layer,///, the  phello-  r           11             1    ■     1 
derm.  Highly  magnified.— After  Van  Tieghe" 

temporarily  inactive. 


:ells  which  had  been 
This  region  is  then  (ailed  the  cambium 
or  secondary  tnerisiem  (see^i  77).  The  divisions  which  ensue 
in    these    cells     are    in    the  main    parallel  to    the  surface   of 


THE   ROOT. 


75 


the    root,  that   is,  they    are 
tangential  divisions. 

The  outer  growing  layer 
or  cork  cambium  is  in  the 
great  majority  of  plants 
formed  from  the  cells  of  the 
pericycle,  but  it  may  be 
produced  by  some  of  the 
cells  of  the  cortex.  In  any 
case  the  tissues  which  arise 
from  this  division  are  of1*" 
such  a  nature  as  to  protect 
the  parts  within.  They  con- 
stitute the  periderm  (fig.  87), 


■Transverse  section  of  two  bundles 
from  the  periphery  of  the  stele  of  root  of  broad 
bean  (/  'icia  Faba)  at  the  beginning  of  secon- 
dary thickening.  The  xylem  bundle,  g,  is 
shaded:  the  phloem  bundle  unshaded.  ?■,  the 
stelar  cambium;  /,  the  pericycle.  aiso  showing 
tangential  divisions  in  parts  ;  s,  the  endoder- 
mis.      Highly  magnified. —After  Haberlandt. 


Fig.  89  Transverse  section  of  thesteleol  root  of  bean  {Pkaseolus  multi/hrus)  shortly 
aftei  set  ondary  thii  ki  ning  has  b<  gun  r,  endodermis;  ,.",  .  peril  yi  le;  /■.  phloem  bundles; 
/,  primary  xylem  bundles;  <_• .  j, ' .  se<  ondarj  xylem;  ,  stelar  cambium;  M,  central  pith. 
Compare  with  fig.  go.     Highly  magnified      Attn  Sachs. 


76 


PLANT  LIFE. 


and  are  ordinarily  cork-like,  i.e.,  thin-walled  and  impervious 

to  water.      Those  cells  which   lie  outside  a  layer  of  cork  are 

therefore  cut  off  from  a  supply  of  food  and  soon  perish. 

The  inner  growing  layer,  or  stelar  cambium,  is  developed 

within   the    stele   and  follows   a 

tortuous  course,  lying  outside  the 

xylem    and    inside    the    phloem 

bundles   (fig.    88).     As  a  result 

of    tangential    divisions    in    this 

region,    tissues   similar   to   those 

already  existing  in  the  stele  are 

produced.       On    the    outer  side 

the     cells     differentiate     mainly 

into  the  tissues  of  the   phloem, 

and    on   the    inner    side    mainly 

the  older  into   those   of  the   xylem,   often 

^/f^S*«Ta1tebre%VcoX"  formin8  a  nearl5'  ^broken  mass 


^Hs'of    each     (figs.    89,    90).      The 

lative  amount  of  the  different 

tissues    which     make    up    these 


ably.     Compare  with  fig.  89,  which 
about  five  times  as  highly  magnified 


b,  b,  b,  b,  four  primary  phioem  bundles;   1  eld 
b',   secondary    phloem    produced    by 
stelar  cambium,  as  are  the  four  wedges 

b^^^^-iSSSfLSft  bundles  goes  far  to  determine 
l!^riS-Af^Semwedges)  the  character  of  the  mature  root. 
87.  (a)  Woody  roots. — If  mechanical  tissues  predominate, 
particularly  in  the  xylem,  the  root  will  become  strong  and 
rigid,  as  in  the  case  of  trees  and  shrubs.  When  the  root  is 
long-lived,  the  activity  of  this  stelar  cambium  is  usually 
resumed  with  each  season,  a  layer  of  tissue  being  thereby 
added  to  the  outside  of  the  xylem  region,  and  a  thinner  layer 
to  the  inside  of  the  phloem.  The  woody  part,  especially, 
shows  in  cross-section  concentric  rings  indicating  the  yearly 
additions.  Since  the  material  produced  by  the  stelar  cam- 
bium usually  greatly  increases  the  diameter  of  the  root,  the 
outside  parts  become  fissured  lengthwise.  Thus,  in  an  old 
and  much-thickened  root  of  the  woody  type,  the  periderm 


THE   ROOT. 


77 


and  the  phloem  region,  with  the  cortex  between  them,  if 
anything  is  left  of  it,  constitute  a  bark,  which  becomes  fur- 
rowed lengthwise,  like  the  bark  of  the  stems  of  many  trees. 
Such  secondary  thickening  finally  produces  in  the  roots  a 


Fig.  91. — .-/,  diagram  of  primary  structure.  /•',  C,  diagrams  showing  the  results  of 
secondary  thickening  from  the  stelar  cambium  in  the  two  extreme  forms  c,  cortex  ; 
<>.•,  endodermis ;  />,  pericycle ;  ph.',  primary  phloem;  //;'',  secondary  phloem;  .1', 
primary  xylem ;  x",  secondary  xylem  ;  cb,  stelar  cambium;  r',  secondary  pith-rays ; 
in,  pith.     After  Van  Tieghem. 

structure  which  is  almost  identical  with  that  of  stems  which 
have  undergone  secondary  thickening.      (Compare  ^[  133.) 

88.  {!')  Fleshy  roots. — but  if  thin-walled  cells  are  the 
predominant  products  of  the  stelar  cambium,  the  root  often 
becomes  very  thick  and  fleshy,  as  in  the  carrot,  turnip, 
radish,  sweet  potato,  beet,  dahlia,  artichoke,  etc.  Such 
roots  serve  the  plant  as  storehouses  of  reserve  food,  and  are 
consequently  useful  to  animals  as  food.  The  thin-walled 
cells  which  are  produced  in  such  volume  may  belong  to  the 
phloem  region,  as  in  the  carrot  and  parsnip,  or  to  the  xylem, 
as  in  the  radish  and  turnip.  This  thickening  for  storage 
purposes  may  affect  either  the  primary  or  secondary  roots, 
or  both.  Other  plants  may  develop  the  cortex  (orchids)  or 
the  pith  (daffodils)  to  an  extraordinary  degree,  forming 
fleshy  roots  which  also  function  as  storehouses. 

89.  (c)  Float  roots.  —  In  plants  which  grow  in  water  or 
in  very  wet  swamps,  roots  are  sometimes  modified  to  serve  is 
floats.      In  these  cases,  the  voluminous  cortex  consists  of  large 


/8  PLANT    LIFE. 

cells,  with  huge  intercellular  spaces  which  are  filled  with  air. 
The  root  thus  serves  to  buoy  up  the  parts  of  the  plant  to 
which  it  is  attached. 

90.  ((/)  Tendrils,  thorns,  etc. — In  a  very  few  plants, 
aerial  roots  are  modified  into  tendrils,  being  slender,  sensitive 
to  contact,  clasping  the  objects  which  they  touch,  if  of 
suitable  size,  and  thus  assisting  the  plant  to  climb  ;  in  some 
instances  they  are  altered  into  thorns,  being  short,  rigid,  and 
sharp-pointed  ;  in  others,  being  exposed  to  the  light,  they 
develop  chloroplasts,  which  enables  them  to  act  as  organs  for 
the  manufacture  of  food. 

91.  Branching. — Both  primary  and  secondary  roots  may 
branch.  The  mode  of  branching  is  of  two  sorts,  either  by 
dichotomy,  or  by  the  production  of  lateral  branches. 

92.  {a)  Dichotomy  occurs  only  in  a  few  fernworts,  whose 
roots  possess  a  single  initial  cell.  In  this  case,  however, 
the  single  initial  cell  (^[  77)  is  not  divided  into  two  equal 
parts  by  a  partition-wall,  as  in  true,  dichotomy  (see  ^|  103), 
but  the  initial  of  the  new  branch  arises  from  a  very  young 
segment  as  in  Metzgeria  (see  fig.  61).  The  result  is  a  fork- 
ing which  cannot  be  distinguished  from  a  true  dichotomy. 

93.  (b)  Monopodial  branching. — In  the  common  mode 
of  branching,  the  monopodial,  the  central  axis  grows  most 
vigorously,  and  bears  lateral  branches  upon  its  sides.  The 
normal  branches  arise  from  lateral  growing  points,  which 
originate  in  regular  succession  behind  the  apical  growing 
point.  But  sometimes  branches  appear  out  of  this  regular 
order.      Such  are  called  adventitious  roots.      (See  *[  76.) 

94.  Position. — Whether  regular  or  adventitious,  the  posi- 
tion of  the  growing  points  is  determined  by  the  vascular 
bundles  in  the  stele,  since  they  originate  opposite  the  xylem 
bundles,  or  with  definite  relation  to  them.  (See  figs.  92, 
93.)  The  number  of  vertical  ranks  of  branches  can,  there- 
fore, be  predicted  with  some  certainty  from  the  structure  of 


THE   ROOT. 


79 


the  root.  While  the  angular  diver- 
gence is  thus  quite  regular,  the  longi- 
tudinal intervals  at  which  the  branches 
will  be  formed,  which  determines 
their  distribution  along  the  length  of 
the  root,  are  unequal  (fig.  92). 

When  secondary  roots  arise  from 
the  shoot,  they  have  a  fixed  relation 
to  the  leaves,  or  they  are  formed 
upon  the  buds  produced  in  the  axils 
of  the  leaves,  or  they  may  arise  at 
indefinite  points  along  the  internodes. 
In  the  first  case,  roots  may  be  pro- 
duced either  opposite  a  leaf,  or  in 
pairs,  right  and  left  of  the  base  of  the 
leaf. 

95.  Origin. — The  origin  of  root- 
branches  and  of  secondary  roots  is 
rarely  exogenous  ;  that  is,  the  root  is 
not  commonly  produced  by  the  divi- 
sion of  cells  which  lie  upon  the  sur- 
face of  a  member.  In  the  great 
majority  of  cases  the  origin  of  the 
roots  is  endogenous  ;  that  is,  the  for- 
mation of  the  root  is  begun  by  the 
division  of  cells  lying  in  the  interior 
of  the  member  producing  it.  In  most 
cases  these  divisions  begin  very  near 
to  the  surface  of  the  stele,  either  just 
without  it,  in  the  endodermis,  or  just 
within  it,  in  the  pericycle.  Soon  a 
growing   point    is    formed     (fig.    93). 


/jr*8*-8" 


X 


The  rootlet  is  thus   ii 
completely      hidden, 


early  stage 


beinj 


buried 


'IG.  92. — Seedling  pea.  showing 
three  \  ei  tii  a)  ranks  ol  brani  li- 
es aloiig  the  main  root.    These 

are  numbered  t,  2, 3.  Natural 
size.— After  Krank. 


So 


PLANT  LIFE. 


beneath  the  cortex,  through  which  it  gradually  makes  its  way 
by  the  destruction  of  the  tissues  ahead  of  it,  partly  through 
disorganization  of  the  tissues  by  pressure,  and,  probably, 
partly  through  actual  digestion  and  absorption  of  the  material 
of  these  cells.  When  the  rootlet  reaches  the  surface  it 
emerges,  therefore,  from  a  distinct  rift  in  the  cortex  (fig.  94). 


Fig.  93 


Fig.  93.— Transverse  section  of  a  root  of  a  fern  (7 '/,•>/.?  cretica),  passing  through  the 
axis  of  a  rootlet  which  has  not  yet  emerged.  Only  the  stele  and  three  rows  of  cortex 
shown,  a,  apical  cell  of  rootlet,  forming  anteriorly  the  root-cap.  <■/>,  and  posteriorly 
the  body  of  the  root,  ec,  e,  c,  pd\  b,  binary  xylem  bundles;  /,  phloem  bundle  with  its 
fellow  opposite;  /V,  pericycle;  at,  endodermis;  /,  temporary  digestive  pouch,  in 
course  of  disorganization  and  digestion;  d,  cells  of  cortex,  which  will  be  disorgan- 
ized as  rootlet  advances.      Highly  magnified— After  Van  Tieghem. 

Fig.  94— The  same  as  fig.  93,  but  older;  not  quite  so  much  magnified.  Tbe'rootlet 
is  just  emerging  from  the  parent  root.  /</,  c,  stele  of  the  rootlet  ;  ec,  its  cortex; 
</,  disorganized  cells  of  cortex,  ec',  of  parent  root;  /-',  secondary  xylem;  other  letters 
as  in  fig.  93.— After  Van  Tieghem. 


96.  External  conditions.  —  Branching  of  the  root  is  often 
profuse,  and  is  dependent  very  largely  for  its  character  upon 
the  conditions  under  which  it  takes  place.  In  those  roots 
which  penetrate  the  soil,  it  is  profoundly  modified  by  the 


THE   ROOT.  8  I 

character  of  the  soil  itself  and  the  amount  of  moisture  and 
organic  matter  in  it. 

97.  Buds. — New  shoots  may  be  formed  by  the  roots,  either 
as  a  result  of  injuries,  or  normally.  In  a  partially  developed 
form,  these  constitute  buds  (see  ^j  101).  Whether  formed 
as  a  result  of  injuries  or  normally,  they  are  known  as  adven- 
titious buds.  They  arise  in  the  same  places  and  develop  in 
the  same  way  as  lateral  roots ;  that  is,  they  are  endogenous, 
and,  as  they  continue  to  grow,  burst  through  the  cortex. 
The  shoots  so  produced  grow  in  the  normal  manner.  Very 
rarely  the  growing  point  of  the  root,  casting  off  the  root- 
cap,  becomes  itself  the  growing  point  of  the  shoot.  This 
alteration  is  usually  the  result  of  artificial  reversal  of  the  posi- 
tion of  the  root,  being  brought  about  in  some  potted  plants 
by  turning  them  upside  down. 


CHAPTER  VIII. 

THE  SHOOT. 

98.  The  gametophyte  shoot. — If  plants  could  be  examined 
in  the  order  of  their  development,  it  would  be  discovered 
that  the  shoot  has  been  evolved  earlier  than  the  root.  It 
makes  its  appearance  first  in  the  leafy  liverworts  and  in  the 
mosses,  in  which  the  gametophyte  and  sporophyte  each  form 
a  stem.  The  gametophyte  differentiates  its  secondary  shoot 
into  a  stem  and  leaves.  This  stem  in  liverworts  is  a  slender 
cylindrical  body  of  very  simple  structure,  upon  whose  flanks 
arise  leaves  which  consist  of  a  single  layer  of  cells  only. 
(See  ^  60. )  Neither  the  stem  nor  the  leaves  are  homologous 
with  the  stem  and  leaves  of  the  higher  plants.  In  the  stem 
itself  one  finds  all  the  cells  practically  alike,  so  that  little 
differentiation  of  tissues  has  yet  occurred.  In  mosses,  how- 
ever, the  gametophyte  stem  shows  some  advance,  in  that  its 
tissues  are  clearly  differentiated,  the  outer  being  transformed 
into  thick-walled  cells,  in  order  to  give  mechanical  rigidity 
to  the  stem,  while  the  innermost,  remaining  slender,  are 
much  elongated  and  serve  the  purpose,  it  may  be,  of  con- 
duction. (See  ^[  63.)  This  differentiation  is  naturally  more 
marked  in  those  mosses  which  are  erect  and  whose  body 
becomes  largest,  since  in  these  the  need  for  rigidity  and  con- 
duction of  food  materials  from  one  part  to  the  other  becomes 
greater.  In  both  groups  the  branching  of  the  gametophyte 
shoot  is  like  that  of  the  sporophyte  shoot  of  some  of  the 
higher  plants,  except  that  the  branches  never  stand  in  the 
same  relation  to  the  leaves.    (See  •'  65.) 

82 


THE    SHOOT.  83 

99.  The  sporophyte  shoot. — The  shoot  developed  by  the 
sporophyte  of  mosses  and  liverworts  forms  no  leaves,  but 
develops  as  a  slender  cylindrical  stalk,  at  the  distal  end  of 
which  the  capsule  containing  the  spores  is  formed  (figs.  64, 
73).  It  is  rather  difficult  to  see  in  this  cylindrical  stalk  the 
homologue  of  the  leafy  stem  developed  by  the  sporophyte  of 
the  fernworts  ana  other  plants. 

The  simultaneous  performance  of  the  work  of  nutrition  and 
of  sexual  reproduction  proved  impracticable,  as  shown  by  the 
development  of  the  liverworts  and  mosses,  which  are  all 
humble  plants.  The  fernworts,  originating  probably  at  an 
early  period  from  the  same  ancestors  as  the  liverworts,  sep- 
arated the  two  functions  and  laid  the  chief  work  of  nutrition 
upon  the  sporophyte.  The  advantage  thus  gained  enabled 
the  extinct  fernworts  to  develop  into  plants  of  tree-like  size, 
and  to  become  the  ancestors  of  all  the  seed  plants. 

The  gametophyte  shoot  was,  comparatively,  a  failure ;  the 
sporophyte  shoot  was  a  marked  success.  It  has  become 
adaptable  to  many  conditions  and  many  functions.  To 
accomplish  this  its  members  have  been  extensively  modified 
in  form  and  structure  in  various  plants.  The  development 
and  mode  of  branching,  together  with  the  various  forms 
which  the  shoot  assumes,  are  now  to  be  discussed,  to  be  fol- 
lowed by  an  account  of  the  two  members,  stem  and  leaf,  into 
which  it  is  usually  differentiated. 

100.  Primary  shoot. —  The  shoot  which  develops  from  the 
fertilized  egg  is  called  the  primary  shoot.  A  very  few  excep- 
tional plants  are  found  in  which  no  primary  shoot  develops, 
although  there  are  a  number  of  cases  in  which  the  primary 
shoot  becomes  early  aborted,  and  its  pla<  e  taken  by  secondary 
shoots  arising  from  the  root.  The  primary  shoot  normally 
arises  in  fernworts  from  the  anterior  half  of  the  egg.  The 
anterior  hemisphere  usually  divides  into  two  quadrants,  one 
of  which  develops  into  the  primary  leaf,  and  the  other  into 


84 


PLANT   LIFE. 


the  primary  stem.  The  stem  quadrant,  by  repeated  divisions, 
quickly  specializes  a  central  cell,  which  becomes  the  apical 
cell  of  the  new  shoot.  Ordinarily  it  takes  the  form  of  a 
three-sided  pyramid,  whose  base  forms  the  extreme  tip  of  the 
developing  shoot  (s,  fig.  76,  /,  fig.  95).  From  the  three  inner 
faces,  as  described  for  the  root  (^f  77),  segments  are  constantly 
formed,  whose  further  divisions  produce  all  the  tissues  which 
constitute  the  members  of  the  mature  shoot,  i.e.,  the  stem 
and  the  secondary  leaves.  In  some  fern  worts  and  in  the  seed 
plants,  the  posterior  hemisphere  resulting  from  the  first  divi- 
sion of  the  egg  grows  into  a  filament  called  the  suspensor, 
and  the  primary  shoot  develops  from  the  anterior  hemisphere. 
(See  fig.  80.)  In  these  plants  ordinarily  two  or  more  cells 
at  the  apex  of  the  primary  shoot  are  specialized  as  the  initial 
cells,  and  from  their  segmentation  arise  the  tissues  of  the 
whole  shoot,  as  in  the  fernworts. 


Fig.  95. — Median  longitudinal  section  through  the  apex  of  a  shoot  of  the  horsetail 
( Eg ui.u •turn.  ,i>  vense),  showing  primary  meristem  and  the  form  of  the  growing  point. 
t,  apical  cell,  from  whi<  h  a  segment,  .V,  has  just  been  cut  off  by  wall/.  S'  ,  a  seg- 
ment previously  cut  off,  has  divided  by  wall  m.  /,/"',/",  successively  older  leaf 
fundaments;  g,  the  initial  cell  of  a  branch.     Magnified  too  diam.— After  Strasburger. 

101.  Primary  meristem. — Whether  the  tip  of  the  shoot 
be  occupied  by  a  single  initial  cell  or  by  a  group  of  initials, 
the  apical   region,    in  which   the   formation  of  new  cells  is 


THE   SHOOT. 


85 


taking  place,  is  called  the  primary  meristem  (fig.  95).  This 
primary   meristem  has    no  definite    limit   below,  but  passes 

insensibly  into  the  permanent  tissues.  The  tip  of  the  shoot 
may  be  either  a  sharp  cone  or  a  low  dome.  Between  these 
forms  a  complete  series  of  gradations  exists.  Below  the  apex 
the  shoot  begins  to  show  a  differentiation  into  a  central  axis 
and  lateral  outgrowths.  The  first  of  these  to  appear  are 
swellings  which  form  the  leaves.  Later,  above  the  leaf 
fundaments  may  appear  the  fundaments  of  the  lateral  shoots. 


Fig.  06. — Diagram  of  a  section  through  a  bud  / ',  the  apex;  i,  2,  3,  4,  successively  older 
leaf  fundaments;  a,  6,  c,  successively  older  branch  fundaments;  </,  e,  vascular  bundles. 
—After  Hansen. 

The  older  leaves  upon  the  sides  of  the  axis  outgrow  the 
younger  ones  and  the  developing  axis,  and  arch  over  them 
in  such  a  way  as  to  form  a  more  or  less  compact  structure, 
which  is  a  terminal  bud.  A  bud  is,  then,  an  undeveloped 
shoot,  whose  older  leaves  protect  the  younger,  and  particu- 
larly the  primary  meristem  (fig.  96).  From  the  terminal 
bud  arise  all  the  members  of  the  primary  shoot. 

102.   Differences  from  root. — From  what   has  been  said  of 
the  origin  of  the  shoot,  it  will   be   observed   that   it   is  dis- 


86 


PLANT   Lli-E. 


tinguished  from  the  root  by  not  forming  through  segmenta- 
tion from  the  outer  faces  of  the  initial  cell  or  cells  a  many- 
layered  epidermal  cap.  In  further  contrast  with  the  root, 
which  often  has  no  true  epidermis  except  the  root-cap,  the 
shoot  is  characterized  by  possessing  an  uninterrupted  epider- 
mis over  its  entire  surface,  consisting  always  at  first  of  a 
single  layer  of  cells.  This  epidermis  persists  as  a  surface 
covering  either  throughout  the  life  of  the  shoot,  or  for  a  long 
period,  being  replaced  only  upon  the 
older  surfaces  of  the  axis  by  subsequently 
formed  protective  layers.  (See  •  134-) 
103.  Branching.  —  branches  of  the 
shoot  arise  from  lateral  buds,  which  are  in 
all  respects  similar  to  the  terminal  buds 
just  described.  If,  for  any  reason,  the 
terminal  bud  of  the  stem  becomes  de- 
stroyed, or  its  growth  arrested,  a  branch, 
developing  from  a  lateral  bud  near  by, 
may  assume  the  position  and  habit  of 
the  main  axis,  its  own  normal  mode  of 
development  being  altered.  In  many 
plants  the  death  or  arrest  of  the  ter- 
minal bud  recurs  at  regular  intervals. 
In  such  plants,  therefore,  the  main  axis 
is  really  a  succession  of  lateral  branches, 
and  the  branching  is  said  to  be  sympo- 
dial  (fig.  97).  In  some  plants,  e.g., 
lilac,  two  lateral  buds  standing  at  the 
same  level  may  develop,  if  the  terminal 
one  fails.  In  this  case  the  shoot  seems 
to  divide  into  two  equal  branches.  This, 
however,  is  not  true,  but  false,  or  sym- 
/>(><Ii\il,  dichotomy.  True  dichotomy,  like  true  dichotomy  of 
the  root,   occurs  only  in  those  plants  in  which   the  axis   has 


I  ig  97.  Shoot  of  Euro- 
pean linden,  t,  the  last 
internode  formed  by  the 
liiid  of  present  season. 
This  dies  and  drops  off 
and  the  shoot  will  be 
formed  next  year  by  the 
last  axillary  bud,  a, 
which  a] ipi  .irs  to  be 
terminal  alter  loss  of  t. 
Half  natural  size.— After 
Frank. 


THE   SHOOT.  87 

a  single  initial  cell.  The  initial  in  these  cases  divides  into 
two  equal  parts,  each  of  which  becomes  the  initial  of  a  new 
branch.  Ordinarily,  however,  the  terminal  bud  develops 
without  interruption.  In  case  it  is  more  vigorous  than  any  of 
the  lateral  buds,  the  plant  will  have  a  central  axis,  from  the  sides 
of  which  distinctly  smaller  branches  arise.  If,  however,  the 
lateral  buds  are  almost  or  quite  as  strong  as  the  central  one, 
the  plant  seems  to  be  broken  up  into  branches,  and,  after  it 
has  attained  its  mature  form,  no  one  can  be  pointed  out  as 
the  main  axis.*  Such  branching  is  monopodia!.  These  two 
types  of  monopodial  branching  and  the  sympodial  type  are 
all  illustrated  in  the  forms  attained  by  common  forest  trees. 
(See  frontispiece.) 

104.  Inflorescence. — Especially  profuse  branching  com- 
monly occurs  in  the  parts  of  the  seed  plants  where  flowers  are 
produced.  Such  clusters  of  branches  bearing  flowers  constitute 
an  inflorescence.  Each  sort  has  received  a  special  name  which 
not  only  indicates  the  type  of  branching,  whether  sympodial 
or  monopodial,  but  also  the  relative  length  of  the  branches. 

If  the  branching  is  monopodial  and  each  lateral  shoot  is 
unbranched,  the  inflorescence  is  a  raceme.  If  the  lateral 
shoots  are  very  short,  it  is  a  spike.  If  the  main  axis  also  is 
very  short,  it  is  a  head.  If  the  main  axis  is  short  and  the 
lateral  axes  long,  it  is  an  umbel.  If  the  lateral  axes  are  of 
unequal  length,  so  as  to  bring  the  flowers  to  about  the  same 
level,  it  is  a  corymb.  If  the  branching  is  sympodial,  various 
forms  of  the  cyme  result.  Several  combinations  of  these 
inflorescences  are  possible. f 

105.  Axillary  buds.— Lateral  buds  are  ordinarily  formed 
in  definite  relation  to  the  leaves.      They  stand  usually  in  the 

*  The  obscurity  is  greatly  increased  by  the  death  of  more  branches  than 
survive,  owing  to  various  causes  resulting  in  poor  nutrition  or  disease. 

f  For  further  discussion  see  Gray:  "Structural  Botany,"  p.  144; 
Goebel :   "  Outlines  of  Classification,"  p.  407. 


88 


PLANT  LIFE. 


upper  angle  formed  by  the  leaf  with  the  stem.     This  angle 
is  known  as  the  axil  of  the  leaf,  and  such   buds  are  said   to 


Fig.  98. 


Fig.  98. — I,  terminal  shoot  of  an  elm.  A,  leaf- 
scars;  k,  axillary  buds.  Natural  size.  II, 
one  of  the  buds  cut  lengthwise  through 
center,  magnified  3  diam.  a,  young  axis; 
.",  li-.it  -.car;  bl,  youDg  leaves;  </■  bud-scales. 
_ — After  Behrens. 

Fig.  99. — .-) ,  twig  of  red  maple  with  ac- 
cessory buds  in  addition  to  axillary  bud. 
B,  twig  ol  butternut,  with  leaf  sear.  «;.  small 
axillary  bud./',  and  larger  accessory  buds, 
1.  d,  above  axil.  Natural  size.  —  After 
Gray. 

Fig.  100.— A  bit  of  stem  of  a  honeysuckle 
(Lonicera  tylosteum)  bearing  large  axillary 
and  smaller  superposed  accessory  buds 
above  the  axils  of  the  scars,  « >i,  from 
which  leaves  have  fallen.  Natural  size. — 
After  Frank. 


be  axillary  (fig.  98).      Ordinarily  a  single  bud  arises  in  the 
axil  of  each  leaf.     Its  origin  is  always  subsequent  to  that  of 

the  leaf- fundament  (figs.  95,  96). 


THE   SHOOT.  89 

There  are  many  cases  in  which  the  lateral  buds  are  not 
found  precisely  in  the  axils  of  the  leaves,  but  slightly  to  one 
side,  or  at  a  greater  or  less  distance  above  the  axil  (figs.  99, 
100). 

106.  Extra-axillary  buds. — Buds  are  frequently  formed 
without  any  relation  whatever  to  the  leaf-axil,  and  even  on 
the  leaf  itself  (fig.  293).  Sometimes  these  extra-axillary 
buds  are  produced  without  the  action  of  any  extraordinary 
cause,  but  more  commonly  injury  of  one  sort  or  another 
seems  to  act  as  a  stimulus  to  the  production  of  such  buds. 
Buds  which  do  not  originate  in  acropetal  succession  on  the 
parent  shoot  are  called  adventitious  buds. 

107.  Adventitious  buds  may  arise  upon  stems,  leaves,  or 
roots.  They  are  most  commonly  and  abundantly  produced 
upon  stems  and  roots.  In  the  willows  their  ready  production 
is  utilized  for  obtaining  young,  vigorous,  and  pliable  shoots 
to  be  used  in  basket-work.  The  few  plants  which  produce 
adventitious  buds  upon  leaves,  as  well  as  the  many  which 
produce  them  on  stems,  are  often  propagated  in  this  way. 
(See  m  364-) 

108.  Dormant  buds. — Many  buds  continue  to  grow  with- 
out interruption  from  the  time  of  their  formation,  but  more 
cease  to  develop  after  they  have  reached  a  certain  stage. 
Such  buds  may  remain  dormant  for  a  considerable  period, 
and  may  even  be  overgrown  and  completely  enclosed  by  the 
wood  upon  old  shoots.  The  bud  in  this  case  grows  slowly 
and  maintains  itself  near  the  surface  of  the  wood.  It  is  quite 
possible  that  these  dormant  buds  should  for  some  reason 
begin  to  develop  later,  when  they  are  liable  to  be  confounded 
with  adventitious  buds.  In  case  they  have  been  buried  by 
the  growth  of  tissues  over  them,  the  shoot  which  they  pro- 
duce will  seem  to  come  from  the  interior  of  the  organ  upon 
which  they  are  borne.  This  apparent  internal  origin  must 
not  be  confounded  with  the  real  endogenous  origin  of  roots. 


90  PLANT  LIFE 

Since  in  most  cases  lateral  buds  have  a  definite  relation  to 
the  leaves,  the  shoots  which  arise  from  them  will  have  a 
similar  relation.  But,  since  many  buds  are  produced  which 
never  develop  into  branches,  this  relation  is  often  obscure 
and  difficult  to  see. 

109.  Special  forms. — The  primary  shoot  may'grow  under- 
ground, in  which  case  its  stem  usually  takes  a  horizontal 
direction  and  becomes  much  thickened  for  storage  of  reserve 
food  (•;  236),  while  its  leaves  are  so  reduced  as  to  be  scarcely 
recognizable.  Such  a  shoot  is  known  as  a  rhizome.  When 
the  primary  stem  is  short,  erect,  and  crowded  with  thickened 
leaf  bases  it  forms  a  bulb,  as  in  the  hyacinth  and  onion. 
When  the  primary  stem  is  short  and  thick,  and  has  thin  scale 
leaves  upon  it,  it  forms  a  conn,  as  in  cyclamen  and  Indian 
turnip. 

Branches  of  the  specialized  primary  shoot  may  be  like  it, 
as  when  some  branches  of  the  rhizome  or  corm  are  them- 
selves rhizomes  or  corms.  Others,  however,  will  be  adapted 
to  other  purposes,  as  when  aerial  branches  arise  from  rhizomes 
to  carry  foliage  and  flowers,  or  when  slender  leafless  shoots 
called  runners  develop  from  the  main  axis  of  the  strawberry 
(fig.  297).  Offsets  and  stolons  (figs.  296,  369)  are  similar 
branches  likewise  adapted  to  propagation  (^[  366). 

Branches  of  the  secondary  shoots  may  also  be  different 
from  their  parent  axis.  In  different  plants  the  shoots  assume 
the  most  varied  forms. 

Such  specialized  branches  may  be  confined  to  a  definite 
region  of  the  plant,  or  may  he  distributed  over  it.  The 
more  important  of  these  kinds  of  branches  may  now  be 
enumerated. 

110.  (a")  Dwarf  branches. — It  is  not  uncommon  to  find 
branches  specialized  merely  by  their  slight  development  in 
length  and  their  capacity  for  being  separated  readily  from 
the  parent  shoot.      Such  short  branches  are  particularly  com- 


THE   SHOOT. 


91 


raon  among  the  cone-bearing   trees.       In   these   plants   the 
snort  branches  carry  the  clusters  of  needle  leaves  (figs.  10 1, 


Fig.  ioi. — A  shoot  of  Scotch  pine  showing  two  regions  of  dwarf  branches  each  with  a 
pair  of  needle  leaves,  and  three  regions  oi  flower  branches;  the  flowers  have  fallen 
From  lower  two,  showing  scale  leaves  covering  the  stem,  Naiur.il  size.— After  Will- 
komm, 


102,    358).      After    the   death  of  the  Leaves  the  branches 
themselves  drop  off.      Somewhat   similar  short   branehes  are 


92 


PLANT  LIFE. 


to  be  recognized  among  many  deciduous  trees,  and,  in  the 
apple,  the   so-called   fruit  spins  arc 
not  dissimilar  (fig.  103). 

111.  (/)  Flowers.  — The  most 
common  of  the  specialized  branches 
among  the  seed  plants  are  those 
which  constitute  the  flower.  In 
these  the  axis  usually  remains  short, 
the  leaves   are    crowded,   and   often 


Fig.  .02.  Fi  .  .03. 

Fig.  102. — The  base  of  leaves  and  dwarf  branch  of  Scotch  pine  cut  through  the  center 
lengthwise.  Besides  the  two  needle  leaves  the  dwarf  branch  carries  a  number  of  scale 
leaves,  d.  Between  the  1  ases  of  the  needle  leaves  is  seen  the  conical  apex  of  the  dwarf 
branch,  showing  their  lateral  origin.     Magnified  about  4  diam. — After  l.uerssen. 

FlG.  103. — Twig  of  apple,  bearing  fruit  spurs.  A,  points  at  which  fruit  was  detached 
the  preceding  year  ;    // ',  leaf  scars.     Natural  size.— After  Hardy. 


some  of  them   are  highly  colored   (fig.    104). 
these  flower  branches  are  deciduous. 


Commonly 


Mag- 


Pic;.   104.  Fig.  105. 

Fig.  104. — Flower  of  Sedum  acre,     s,   sepal;  /,  petal;   si,  stamen;  c,  carpel 

nified  3   diam— After  Uaillon. 
FlG.    105. — Piece  of  a  twig  nf  asparagus  ;  in   the   axil  of  the  scale  leaf,  b,  arise  a  (lower 

shoot,  and  three  leafless  needle-like  branchlets.    Magnified  about  2  diam. — After  Frank. 

112.    (c)    Cladophylls. — A    few    plants    have    developed 
shoots  which  replace   leaves  in   function  and  resemble  them 


THE   SHOOT.  93 

In  form.  These  cladophylls  may  be  either  broad  and  flat- 
tened, as  in  the  "smilax"  of  the  greenhouses,  or  they 
may  be  slender  and  needle-like,  as  in  the  common  garden 
asparagus  (fig.  105).  In  any  case,  since  they  replace  leaves 
in  function,  they  are  abundantly  supplied  with  green  color- 
ing matter  for  manufacturing  food. 

113.  (</)  Bulblets. — Other  branches  remain  undeveloped 
as  buds,  but  their  leaves  become  thick  and  fleshy.  These 
bulblets  are  easily  detached  and  serve  for  propagation.  (See 
^|  364.)  They  are  to  be  found  in  many  plants.  In  the 
tiger-lily  they  occupy  the  axils  of  the  leaves  (fig.  294), 
and  are  modified  lateral  buds,  while  in  the  garden  onion 
they  usually  replace  the  flowers. 

114.  (c)  Tubers. —Some  underground  shoots  have  their 
ends  suddenly  and  greatly  enlarged,  adapting  them  to  the 
storage  of  food.  They  are  then  called  tubers.  In  the  white 
potato  the  tuber  consists  of  several  terminal  internodes  of 
an  elsewhere  slender  underground  stem,  the  "eyes"  being 
lateral  buds  in  the  axils  of  minute  scale  leaves.  In  a  few 
plants  tubers  may  even  be  formed  above  ground,  as  in  certain 
polygonums  whose  flowers  are  often  replaced  by  little  tubers 
which  are  readily  detached  (fig.  106). 

115.  (/)  Tendrils.— Some  shoots  take  the  form  of  slender, 
leafless,  sensitive  tendrils,  which  assist  the  plant  in  climbing 
by  coiling  about  suitable  objects  (fig.   107). 

116.  (g)  Thorns. — Many  plants  produce  defensive  shoots, 
which  are  leafless,  rigid,  short,  and  sharp,  called  thorns, 
which  may  be  either  simple  or  branched  (fig.  108).  The 
honey-locust  furnishes  an  excellent  example  of  branched,  or 
compound,  thorns. 

Leaves  themselves  may  be  developed  as  tendrils  or  as 
thorns,  so  that  it  must  not  be  assumed  from  appearance  alone 
that  such  members  are  forms  of  the  shoot.  Observation  of 
the  origin  and  relation   of  the  members  will  reveal  their  true 


94 


PLANT  LIFE. 


nature.      If  shoots,  they  will   usually  be  subtended  by  a  leaf; 

if  leaves,  they  will  often  have  a  bud  or  a  shoot  in  their  axils. 
Thorns  or  tendrils  which  do 
not  arise  at  the  nodes  are 
reckoned  as  shoots. 

117.  Duration. — Shoots  are 
either  annual,  biennial,  or  per- 
ennial.     If  the  entire  shoot  dies 


Fig.  106. 

Fig.  106.—.-!,  upper  part  of  a  plant  of  Polygonum  viviparum,  showing  flower  cluster, 
the  flowers  in  lower  hall  being  replaced  by  tubers.  Two-thirds  natural  size.  /.',  a 
fallen  tuber.  Magnified  about  3  diam.  C,  a  plantlet  growing  from  tuber.  Natural 
size.— After  Kn  ni  1 

Fig.  107. — A  portion  of  the  stem  of  white  bryony,  />',  from  which  a  tendril,  ».>-,  arises 
near  the  leaf  stalk,  />,  and  the  bud,  k .  11,  rigid  portion  of  tendril  ;  the  portion  between 
11  and  tlu-  portion  .1,  clasping  the  support.  A,  has  become  coiled  into  a  spiral  which 
reverses  the  direction  oi  the  coils  at  w  and  «/'.     Nearly  natural  size.— After  Sachs. 

this  generally  involves  the  death  of  the  whole  plant,  though 
new  adventitious  shoots  may  arise  from  the  roots,  as  in 
sweet    potatoes.      In   many  plants,  in  which  the  shoot  seems 


THE   SHOOT.  95 

to  die  at  the  close  of  the  growing  season,  an  underground 
portion  really  survives,  and  sends  up  the  new  shoots.  Such 
plants,  if  they  live  for  two  years,  are  called  biennials ;  or, 
if  they  live  for  several  or  many  years,  are  called  perennials. 


Fig.  108. — Shoots  of  Vella  sfiinosa,  showing  thorns.     Natural  s 


The  shoot  may  be  composed  mainly  of  soft  tissues,  and 
persist  underground,  where  it  is  protected  against  unfavorable 
conditions,  such  as  drought  and  cold,  and  especially  against 
sudden  changes;  or  it  may  be  composed  mainly  of  mechan- 
ical tissues,  and  be  fully  exposed,  as  are  the  shoots  of  trees. 
In  these  cases  the  leaves  generally  perish  and  drop  off  an- 
nually, but  in  the  "evergreen"  plants  they  live  more  than 
one  growing  season. 


CHAPTER    IX. 

THE  STEM. 

118.  Definition. — The  shoot  is  almost  always  segmented 
into  members  of  two  kinds,  the  stem  and  leaves.  The  stem 
is  the  central  axis  of  any  shoot,  and  the  leaves  are  lateral  out- 
growths, or  branches,  of  it.  These  two  members  cannot  be 
accurately  defined,  but  are  in  most  cases  readily  distinguish- 
able. Leaves  commonly  differ  from  the  stem  in  internal 
structure,  and  in  their  flattened  form,  limited  growth,  and 
position,  subtending  the  lateral  shoots.      (See  further  p.  117.) 

119.  Nodes  and  internodes. — Upon  examining  the  surface 
of  the  stem,  it  is  almost  always  readily  distinguishable  into 
distinct  regions,  the  nodes  and  internodes.  The  nodes  are 
the  narrow  zones,  often  somewhat  swollen  (whence  the  name), 
at  which  one  or  more  leaves  arise.  The  internodes  are  the 
zones  between  the  nodes.  Upon  watching  the  development 
of  the  stem  from  the  terminal  bud,  it  will  be  seen  that  new 
nodes  and  internodes  are  constantly  emerging  from  its  base, 
and  that  the  leaves  formed  at  the  nodes  are  successively 
expanding.  This  emergence  of  the  internodes  is  due  to  their 
elongation.  The  amount  of  elongation,  however,  varies 
greatly  in  different  plants,  and  even  in  different  parts  of  the 
same  plant.  In  many  cases  the  internodes  are  considerably 
and  uniformly  elongated  ;  the  leaves  are  then  distributed 
along  the  stem  at  considerable  and  regular  intervals.  In  other 
cases  the  internodes  remain  very  short,  and  the  leaves  are, 

96 


THE    STEM.  97 

therefore,  crowded.   They  may  be  so  crowded  as  to  completely 

envelop  the  stem   and  hide   it 

from  view.     This  is  well  seen 

in  the  scale-like  leaves  of  such 

plants  as  the  pines  (fig.   101), 

cedars,  and  arbor  vitas  (fig.  109). 

Or,  certain  of  the    internodes 

may     elongate,     while     others 

remain       undeveloped.         For 

example,     in    the     shepherd's- 

purse,      the      first      internodes 

remain  short,  so  that  the  lower 

leaves    are    Crowded  intO     a    tuft   FlG    >°9—A  shoot  of  arbor  vita;  or  white 

cedar,   showing    scale    leaves    covering 
Of  rosette;    the    following  inter-      stem-     Natural  size.— After  Kerner. 

nodes  are  elongated,  the  corresponding  leaves  being  scattered 
at  regular  intervals;  while,  still  higher,  the  internodes  are 
again  shortened  and  the  leaves  brought  into  close  clusters  in 
the  flowers. 

120.  The  consistence  of  the  stem  depends  upon  the  relative 
amount  of  mechanical  tissues  which  it  contains.  Stems  may 
be  designated  as  woody,  solid,  or  fleshy,  terms  which  need  no 
further  definition. 

121.  The  shape  of  the  stem  varies  extremely  in  different 
plants.  Very  commonly  the  stem  as  a  whole  is  looked  upon 
as  cylindrical,  but,  if  carefully  considered,  it  will  be  seen  that 
the  diameters  of  successive  internodes  at  first  become  gradually 
greater,  and,  after  maintaining  this  maximum  for  a  time,  grow 
gradually  less.  The  stem  is,  therefore,  a  cylinder  with  more 
or  less  conical  ends.  If  the  attainment  of  the  maximum 
diameter  is  sudden,  and  the  diminution  similarly  sudden,  the 
resulting  stem  will  have  the  shape  of  a  double  cone.  The 
modification  of  such  a  form  into  the  spherical  is  not  diftic  nit 
to  imagine.  Striking  illustrations  of  these  extreme  forms  are 
to  be  found  among  the  cactuses  (fig.   no). 


93 


PLANT  LIFE. 


122.  A  section  of  the  stem  commonly  presents  an  irregu- 
larly circular  outline  (fig.  in).  Occasionally  the  surface  of 
the  stem  is  fluted  or  channeled,  and,  if  these  grooves  or 
channels  be  few  and  the  corresponding  angles  prominent,  the 
section  of  the  stem  is  polygonal,  with  three,  four,  five,  six,  or 
more  sides. 

123.  Habit. — As  to  habit,  stems  are  commonly  erect  when 
enough  mechanical  tissue  is  developed  to  render  them  suffi- 
ciently rigid  to  carry  not  only  their  own  weight,  but  that  of 


Jmw^ 


A  B 

Fig.  iio. — Cactuses,  showing  form.  A,  Cereus  dasyacanthus.  B,  Echinocactus 
horizontalis.  In  both  the  clusters  of  spines  arise  from  tubercles  on  the  stems. 
Reduced. — After  Kerner. 

the  leaves  and  other  members  attached  to  them.  Other  stems 
lie  flat  upon  the  ground,  to  which  they  may  or  may  not  attach 
themselves  by  the  development  of  secondary  roots.  Between 
these  prostrate,  or  creeping,  stems  and  the  erect  form  every 
conceivable  position  exists.  The  direction  of  growth  is  deter- 
mined largely  by  the  relation  of  the  plant  to  gravity  and  light 
as  stimuli.      (See  ■  •;  285,  287.)     Other  stems  rise  into  the 


THE    STEM. 


99 


air,  not  by  their  own  rigidity,  but  by  the  development  of 
special  members  for  climbing  purposes,  such  as  recurved 
spines,  tendrils,  sensitive  leaf  stalks,  or  even  by  recurved 
normal  branches.  (See  ^[^[115,  158.)  Others  wrap  them- 
selves about  objects  of  suitable  size,  and  are  called  twining 
stems.  (See  •  291.)  The  direction  of  twining  varies  with 
different  plants,  but  most  commonly  corresponds  to  the 
movement  of  the  hands  of  a  watch,  the  support  being  sup- 
posed to  be  in  the  center. 

124.  Primary  structure. — The  origin  of  the  stem-tissues 
has  already  been  described.      (See  ^j  100.) 

In  following  the  stem  from  apex  to  base  it  is  readily 
observed  that  the  structure  changes  as  the  parts  grow  older. 
It  is  possible,  however,  to  select  a  point  at  which  the  stem  in 


Fig.  hi.  Fig.  i  12. 

Fig.  hi.     Diagram  ol  a  transverse  section  of  stem  of  Iberis  amara,  showing  outline, 

and  paired  \  asi  ular  bundles.     The  bla<  k  is  the  xylem  bundle  :  the  gray  is  the  phloem 
bundle.    The  outer  line  represents  the  epidermis  :  a  circle  including  the  bundles  would 
mark  the  limits  ol  the  stele,  with  its  1  entral  pith  :   the  cortex  lies  between  the  epid«  in  is 
and  stele       Vftei   Ntfgeli 
Fig.  1  (2.— Diagram  of  a  transverse  section  ol  a  palm  stem     The  epidermis  is  represented 

by  the  outer  line;   the   endodermis   by  the   innei    one,  with  the   narrow  CO  It  ex    between 

them;   the   stele,  with   numerous  bundles   scattered  through  the   pith,  is  within  the 
endodermis.     Alter  Frank. 


all  cases  attains  a  definite  development.  This  point  is  at  the 
internode  whi<  h  has  just  reached  its  full  length.  The  struc- 
ture of  the  stem  at  this  point  may  be  designated  as  its  primary 
structure.     If  a  thin  section  be  cul  from  such  an  internode, 


IOO  PLANT  LIFE. 

three  definite  regions  may  be   distinguished,  viz.:    (i)  the 

epidermis;   (2)  the  cortex;  (3)  the  stele  (figs,  in,  112). 

125.  1.  The  epidermis. — This  is  a  single  layer  of  cells 
forming  the  extreme  edge  of  the  section,  being,  therefore,  the 
layer  which  covers  the  surface  of  the  stem.  Here  and  there 
maybe  observed  intercellular  spaces,  which  permit  communi- 
cation between  the  outside  air  and  similar  spaces  in  the  deeper 
tissues  of  the  cortex.  These  openings  are  usually  bordered 
by  two  specialized  cells,  and  are  called  stomata.  The 
epidermal  cells  may  be  furnished  with  green  chlorophyll 
bodies,  or  these  may  be  entirely  absent. 

126.  2.  The  cortex. —  This  region  consists  of  several 
rows  of  cells,  usually  thin-walled  and  not  in  close  contact,  and 
hence  abundantly  provided  with  intercellular  spaces.  These 
cells  usually  contain  many  chlorophyll  bodies,  to  which  the 
green  color  common  to  stems  is  due. 

The  innermost  layer  of  the  cortex  abutting  upon  the  stele, 
whose  radial  walls  are  suberized  (^J  9),  is  usually  specialized 
to  form  a  distinct  layer  of  cells.  This  layer  is  the  endodermis 
(fig.  1 1 8). 

127.  3.  The  stele. — The  central  region  is  called  the 
stele.  It  consists,  as  in  the  root,  ordinarily  of  three  parts. 
Its  outer  layer  of  cells  is  known  as  the  pericycle  (fig.  118). 
Within  the  pericycle  are  clusters  of  smaller  cells,  the  cut  ends 
of  the  vascular  bundles.  Occupying  the  space  between  the 
vascular  bundles  is  the  pith  (figs,   in,   112). 

These  regions  of  the  stem  are  subject  to  various  modifica- 
tions. 

128.  1.  The  epidermis. — While  the  epidermis  is  usually 
a  single  layer  of  cells,  it  is  sometimes  increased  to  two  or 
three  layers.  Stomata  may  be  entirely  lacking.  This  is 
especially  the  case  in  those  underground  and  submerged 
stems  in  which  the  stomata  would  be  useless.  The  cells  of 
the  epidermis  are  often  prolonged  into  outgrowths  of  various 


THE    STEM. 


101 


shapes,   such  as  hairs,  scales,   and  the  like   (figs.    113,  114; 
see  also  figs.  361-365). 

129.  2.  The  cortex. — In  some  plants  the  cortex  under- 
goes an  enormous  development,  forming  in  some  tubers  the 
greater  part  of  the  massive  stem. 
In  other  plants  the  cortex  under- 
goes such  reduction  that  it  con- 
sists only  of  two  or  three  layers  of 
cells.  It  very  commonly  enters 
with  the  epidermis   into  the   for- 


FlG.    113 


Fig.  113. — Forms  of  hairs  from  Plectranthus.  a,  simple  pointed  hair;  /•,  stalked 
glandular  hair;  < ,  sessile  glandular  hair  with  secretion  covering  the  two  glandular 
cells.     Highly  magnified. — After  De  Bary. 

Fig.  114. — T-shaped  hair  of  the  wall-rlower  [Cheiranthus).  e,  epidermis.  Highly 
magnified. — After  De  Bary. 


mat  ion  of  outgrowths,  which  are  then  known  as  emergences. 
These  emergences  may  take  the  form  of  rounded  elevations, 
producing  a  warty  stem,  or  they  may  be  sharp  pointed 
and  either  straight  or  curved,  forming  prickles  (figs.  115, 
116);  or  the  emergence  may  be  produced  along  a  con- 
tinuous line,  giving  rise  to  wings  upon  the  stem  ;  or  the 
stem  may  be  more  or  less  covered  with  large  pointed  or 
angular  elevations,  called  tubercles,  as  in  some  cactuses 
(fig.  no).  Very  frequently  the  intercellular  spaces  of  the 
cortex  are  greatly  enlarged,  forming  air  passages  of  con- 
siderable size.  These  passages  may  arise  by  mere  separation 
of  the  cells  of  the  cortex,  or  by  the  destruction  of  those  in 
certain  regions,  or  by  a  combination  of  these  causes 
(fig.    117).       In    other    cases    the    cortical    cells,    instead    of 


PLANT   LIFE. 


remaining    thin-walled,   may   become    greatly    thickened    in 
certain    regions,    or    even    throughout    the    cortex.       These 


Fig.   115.  Fig.   116. 

Fig.   1 15 —Prickles  on  the  stem  of  a  rose.     Natural  size.— After  Prantl. 

Fig.   116.—  A  longitudinal  section  through  a  rose  prickle  in  a  young  stage,  showing  Imu 

the  sub-epidermal  (cortical)  tissues  enter  into  the  structure  of  the  emergence.     Magni 

fied  200  diam. — After  Rauter. 


Fig.  117. — Transverse  section   of  the  Stem  of  Elatine,  showing  intercellular  canals,  r. 
Magnified  about  15  chain.— After  Reinke. 

mechanical  cells  are  likely   to  be  aggregated  in  clusters  or 
strands,    and   serve   an    important    purpose   in   strengthening 


THE   STEM. 


103 


the  tissues  (fig.  118).  In  some  cases  vascular  bundles  arc 
found  in  the  cortex  outside  the  stele,  when  they  are  known 
as  cortical  bundles. 


Fig.  118.— Transverse  section  of  the  stem  of  a  ground  [>ine  (Lycoiodium  complana- 
tinu).  The  stele  is  enclosed  by  the  endodermis,  en\  />,  pericycle;  »'.  xylem  bundle; 
///,  phloem  bundle;  cc',  cortex,  . '.  mechanical  tissue  with  thickened  walls;  <■/,  epi- 
dermis. In  the  cortex  a  branch  stele  passing  out  to  a  leaf  c.n  the  right  is  cut  across. 
Magnified  ioo  diam.— After  Sachs. 

130.  3.  Stele.  (</)  Pericycle. — The  pericycle  is  rarely 
wanting.  It  is  much  more  frequently  increased  from  one  to 
several  layers  of  cells.  In  this  case  it  commonly  differ- 
entiates into  regions  of  mechanical  cells  with  thick  walls  and 
small  cavities  and  a  region  of  thin-walled  cells.  These 
mechanical  cells  are  either  aggregated  in  strands  opposite  to 
the  vascular  bundles  of  the  stele,  or  they  constitute  a  com- 
plete zone  around  it.  Many  of  the  most  valuable  textile 
fibers,  such  as  those  of  tlax,  hemp,  and  ramie,  are  obtained 
from  this  region  of  the  stem  (fig.   1 19). 

131.  (/')  Vascular  bundles. — In  any  section  of  the  stem 
the  number  of  vascular  bundles  in  the  central  cylinder  varies 
greatly,  not  only  in  different  plants,  but  c\cn  in  different 
parts  of  the  same  plant.    The  bundles  are  commonly  arranged 


104 


ri.AA'T    LIFE. 


in  pairs,  a  phloem  (bast)  bundle  and  a  xylem  (wood)  bundle 
being  placed  side  by  side,  thexylem  occupying  the  side  next 


Fitt.  i  ic).— Portion  of  a  transverse  section  of  the  stem  of  flax,  m,  pith;  //.secondary 
xyiern  forming  a  woody  cylinder;  pk,  phloem  ;  />,  bundles  of  mei  hanical  tissue  (fibers) 
among  the  thin-walled  cells,  tin- two  sorts  making  up  the  cortex;  ./,  the  epidermis. 
Magnified  about  J5  diam. — After  Frank. 

P 


Fig.  120. — Transverse  section  of  a  bundle  pair  from  the  stem  of  .1  begonia.  'The  shaded 
pari  is  the  xylem  bundle;  the  small  irregular  cells  above  are  the  phloem  bundle; 
between  them  is  a  zone  "t  urmi.itiiii:  1  •  inn    tern),  the  stelar  cambium, 

ulii.  Ii  extends  also  right  and  left  oi  the  bundle  pair.    The  radius  of  the  section  passes 
through  (V;  C,  next  the  center.     Magnified  150  diam.— After  Haberlandt. 

the   center  of  the  stem,  and   the  phloem  the  side  next  the 
surface  (figs.  1 1 1,  120).      The  number  and  position  of  these 


THE   STEM. 


105 


bundles  is,  however,  subject  to  change.  In  some  cases 
one  of  the  strands  surrounds  the  other.  Commonly  it 
is  the  bast  which  surrounds  the  wood,  as  in  the  fernworts 
(fig.    121).       Sometimes    independent    phloem    bundles    are 


Fig.  121. — Transverse  section  of  Selaginella,  showing  three  steles,  eacli  composed 
of  a  xylem  bundle  surrounded  by  phloem.  /,  /,  intercellular  spaces  in  cortex, 
separated  from  the  steles  only  by  the  large-celled  endodermis  The  cells  underlying 
the  epidermis  are  thickened  to  form  mechanical  tissue.  Magnified  150  diam.— After 
Sachs. 

found  with  which  are  associated  no  xylem  bundles.  In 
the  phloem  certain  cells  may  develop  into  libers,  which 
are  not  to  be  confused  with  the  fibers  occurring  in  the 
pericycle.  Some  of  these,  also,  are  valuable  in  the  textile 
industries. 


io6 


PLANT  LIFE. 


The  paired  vascular  bundles  within  the  stele  occupy  various 
positions,  and  for  purpose  of  location  may  be  spoken  of  as 
though  single.  If  transverse  sections  of  the  stem  are  ob- 
served, they  may  be  seen  either  in  a  single  row,  roughly 
parallel  with  the  surface  of  the  stem  (fig.  in),  or  in  several 
concentric  rows  (fig.  122),  or  they  maybe  irregularly  dis- 
posed throughout  it  (fig.   112).      No  one  method  ofarrange- 


Fig.  122.— Transverse  section  of  the  aerial  stem  of  an  onion  (A  Ilium  Schoenoprasum). 
e,  epidermis;  ch,  chlorophyll-bearing  tissue  of  cortex;  r,  colorless  tissue  of  cortex; 
C,  c'.  vascular  bundles  (xvleni  bundles  black,  phloem  bundles  dotted);  sr,  mechanical 
tissues  connected  into  a  cylinder;  m,  pith;  A,  pith  canal  formed  by  destruction  of 
1  ells.      Magnified  30  diam. — After  Sa<  lis. 

ment  is  confined  to  any  of  the  larger  groups  of  plants, 
although  the  first  is  characteristic  of  most  dicotyledons, 
while  both  the  second  and  third  methods  are  common  among 
the  monocotyledons.* 

*  So  many  exceptions  are  found  to  these  last  statements  that  it  is  lust 
not  to  indicate  the  arrangemenl  of  the  bundles  by  the  terms  dicotyle- 
donous or  monocotyledonous,  as  has  been  commonly  dune  ;  nor  is  it 
possible  to  maintain  the  terms  exogenous  and  endogenous,  which  have 
long  since  become  obsolete  because  misleading. 


THE   STEM. 


107 


h     likewise     varies     greatly   in 

to     different     conditions     of 

found    enormously     developed 


as  in   some    tubers,  such    as 
In  other  plants,  particularly 


132.  (c)    Pith.— The    1 

different  plants  according 
growth.  It  is  frequently  found 
in  those  parts  of  the  stem  which  are  used  by  the  plant 
for  storing  its  reserve  food, 
the  white  potato  and  the  yam. 
those  growing  in  water,  it 
suffers  extreme  reduction  or  is 
often  completely  wanting,  in 
which  case  the  bundles  of  the 
stele  are  in  close  contact,  and 
the  cortex  usually  shows  a  cor- 
responding increase.  In  other 
plants  the  cells  constituting 
the  pith  are  greatly  thickened, 
so  as  to  form  a  mechanical 
tissue.  The  thickened  areas 
are  usually  either  opposite  the 
bundles,  forming  a  strand 
closely  adherent  to  their  inner 
faces,  or  they  may  extend  to 
the  flanks  of  the  bundles,  thus 
forming  an  arc  embracing 
each.  Sometimes  the  thickened  region  becomes  extended 
between  the  bundles  and  joins  the  corresponding  mechanical 
tissues  in  the  pericycle,  or  even  those  of  the  cortex,  so  as  to 
enclose  completely  the  individual  bundles  (fig.  123).  In 
other  plants  the  pith  dies  early  and  shrivels  up.  Very  large 
canals  may  thus  be  formed  through  it,  or  it  may  even  dis- 
appear entirely  (fig.  122).  Such  early  disappearance  of  the 
pith  produces  the  hollow  stem  characteristic  of  the  grasses, 
the  sedges,  and  the  various  members  of  the  sunflower  family. 

133.  Secondary  structure. — Some  stems  retain  throughout 
their  entire  existence  the  primary  structure  which   has  just 


Fig.  123. — Transverse  section Ol  .1  bundle- 
pair  of  Indian  corn.  r>,  phloem  bundle; 
1.  %\g,  s,  r,  xylem  bundle:  p.  pith;  /, 
an  intercellular  space  formed  by  the 
tearing  of  some  of  the  .xylem  tissues. 
The  bundle  pair  is  surrounded  by  a 
sheath  of  thick-walled  mechanical 
tissues.  Magnified  235  diam.  —  After 
Sachs. 


io8 


PLANT  LIFE. 


been  described,  undergoing  only  slight  changes  in  the  char- 
acteristics of  the  individual 
tissues  which  compose  it. 
Thus,  with  age,  there  may  be 
a  thickening  of  the  tissues  so 
as  to  impart  greater  rigidity  ; 
or  the  waterproofing  of  the 
exterior  may  be  made  more 
perfect.  These  and  similar 
changes  do  not,  however, 
materially  alter  the  structure. 
This  permanence  of  primary 
structure  is  particularly  fre- 
quent in  the  stems  of  mono- 
cotyledonous  plants.  It  has 
been  observed  also  in  some 
dicotyledonous  plants;  for  ex- 
ample, in  the  white  water  lily. 
But  the  stems  of  the  great 
majority  of  dicotyledonous 
plants,  as  well  as  the  conifers, 
quickly  lose  their  primary 
structure,  adding  tissues  of 
considerable  amount,  so  as  to 
bring  about  a  more  or  less 
striking  rearrangement  of  the 
iun  of  first  formed  tissues  (fig.  124). 
S^Xc^tgh°nAtf^Tep1-      134-  Secondary  meristem.- 

SftA  strSft  xiKSS  This  modification  of  the  struct- 

^^r^r^V^Z^r;;,:  "re  of  the  stem  is  due  chiefly 

SS^i&S.  ^SSHSLH  to  the  formation  of  one  or  two 

AftcrTsd,iri1'  layers    of    actively     dividing 

cells,     which    constitute    secondary    meristem    or    cambium, 

roughly  parallel  to  the  surface.     When  there  are  two,  one  of 


THE    STEM. 


IO9 


the  layers  of  cambium  arises  nearer  the  (enter,  the  other 
nearer  the  periphery  of  the  stem.  They  are  formed  from 
existing  cells  which  resume  their  power  of  active  growth 
and  division.  The  development  of  the  tissues  from  the  ex- 
ternal meristem,  or  cork  cambium,  results  in  the  formation 
of  the  periderm,  while  the  tissues  arising  from  the  internal 
meristem,  or  stelar  cambium,  form  the  secondary xylem  and 
phloem  (fig.   124). 

135.  1.  The  formation  of  secondary  cortex. — As  the 
cells  of  the  external  meristem  divide,  sometimes  the  outer 
segments  and  sometimes  the  inner  ones  differentiate  into 
permanent  tissues,  while  the  other  segment  remains  as  an 
initial  for  the  next  division.  Some  of  the  secondary  tissue 
thus  produced  lies  outside  of  the  generating  layer,  and  some 
inside  (fig.  127).  The  secondary  tissues,  as  a  whole,  con- 
stitute the  periderm. 


Fig.  125. — A  bit  of  a  transverse  section  of  a  young  stem  of  Scutellaria  silendens  at 
the  beginning  of  tin-  formation  .if  periderm.  <■,  epidermis,  some  of  its  cells  divided  by 
tangential  walls,    c,  cortex.     See  tie    126.     Highly  magnified.— After  Haberlandt. 

FlG.  126.— Same  as  125  but  older.  <•,  outer  half  of  epidermal  cells;  k,  cork  cells  formed 
by  tangential  divisions  of  inner  half  of  epidermal  cell  (fig.  125)  which  has  become  pk, 
the  cork  cambium;  ,,  cortex.      Highly  magnified.— Alter  Haberlandt. 

136.  Periderm. — -The  tissues  formed  inside  the  cambium 
{phellodernt)  are  usually  similar  to  the  cells  of  the  primary 
cortex.  They  form  intercellular  spaces,  and  retain  their 
living  contents,  among  which  chloroplasts  are  often  present. 
W  ith  the  thickening  of  the  outer  tissues,  however,  these 
usually  disappear. 


IIO  PLANT   LIFE. 

The  outside  tissues  of  the  periderm  rarely  remain  living 
No  intercellular  spaces  arise  between  the  flat  cells,  which 
early  lose  their  contents,  while  the  walls  become  waterproof. 
Such  a  tissue  is  known  as  cork  (fig.  128).  Other  cells  may 
be  altered  into  mechanical  tissues  by  the  thickening  of  their 
walls  and  the  death  of  the  protoplasm.  Zones  of  cork  often 
alternate  in  the  periderm  with  zones  of  mechanical  tissues 
Since  no  water  solution  can  pass  through  a  cork  zone,  it  is 
evident  that  all  parts  lying  outside  of  one  are  cut  off  from  a 
supply  of  nourishment,  and  must  therefore  perish  sooner  or 
later. 

137.  Location  of  cork  cambium. — How  much  will  thus  be 
killed  depends  upon  the  position  of  the  layer  of  cells  which 


Fig.  128. 

Fir..  127. — Part  of  a  transverse  se<  don  through  the  cork  cambium  and  the  tissues  ii  pro- 
duces  in  the  European  elm.  k,  cork  cells,  the  innermost  layer  still  with  some  proto- 
plasmic contents;  pk,  cork  cambium;  pd,  secondary  cortex.  Highly  magnified. — 
\1te1  Haberlandt. 

Fig.  128.— Part  of  a  transverse  section  of  young  stem  of  cherry,  showing  formation  of 
periderm,  e,  epidermis;  k,  cork;  ///.  cork  cambium,  with  one  row  of  secondary 
cortex  below;  ,,  cortex.      Highly  magnified.  — After  Haberlandt. 


becomes  the  generating  layer.  It  may  be  formed  in  one 
of  three  places:  (a)  It  is  sometimes  in  the  epidermis  itself 
(fig.  125),  in  which  case  only  the  outer  half  of  the  epidermal 


77//-;    STEM.  HI 

cells  will  be  sloughed  off.*  (/>)  In  a  majority  of  cases  the 
generating  laver  of  the  periderm  is  formed  in  the  cortex, 
either  immediately  under  the  epidermis  (fig.  128)  or  in  one 
of  the  deeper  layers  (fig.  127).  (c)  In  other  instances  the 
generating  layer  is  formed  in  the  pericycle.  If  the  pericycle 
is  more  than  one  layer  of  cells  thick,  it  may  be  formed  in 
the  innermost  or  in  any  one  of  the  external  parts.  In  this 
case,  therefore,  there  will  be  killed  all  the  tissues  of  the 
cortex  and  any  of  the  stelar  tissues  which  lie  outside  the 
portion  of  the  pericycle  from  which  the  generating  layer  is 
formed. 

138.  Perennials. — Plants  which  live  for  a  single  year  have 
usually  but  a  small  amount  of  periderm  formed,  or  sometimes 
none  at  all.  In  those,  however,  which  are  perennial,  peri- 
derm is  formed  not  only  during  the  first  year's  growth,  but 
the  activity  of  the  generating  layer  is  resumed  at  the  begin- 
ning of  succeeding  seasons,  so  that  annual  additions  are 
made  to  it.  In  the  cork  oak,  for  example,  there  is  an  extraor- 
dinary development  of  cork,  which  becomes  so  thick  and 
is  so  resistant  to  the  passage  of  water  that  it  serves  for  the 
manufacture  of  stoppers.  In  the  bottle-cork  mechanical 
tissues  occur,  not  in  zones,  but  in  isolated  patches,  forming 
the  gritty  masses  in  poor  corks. 

139.  Secondary  periderm. — The  dead  tissues  which  accu- 
mulate from  year  to  year  upon  the  outside  of  perennial  stems 
constitute  a  large  part  of  what  is  known  as  the  bark.  In  the 
bark  of  most  trees  one  or  more  generating  layers  form  in 
addition  to  the  first,  giving  rise  thus  to  secondary  periderm 
(fig.  129).  The  secondary  periderm  may  be  either  concentric 
with  the  first,  in  which  case  the  outer  parts  of  the  bark  will 
be  made  of  concentric  layers  which  separate  readily  from 
each  other ;   or  the  new  generating  layer  may  intersect  the 

*  The  epidermis  sometimes  continues  to  grow  for  many  years,  while  a 
secondary  cortex  is  formed  under  it.      In  this  case  no  sloughing  oft  occurs. 


112  PLANT  LIFE. 

outer  one,  so  as  to  isolate  a  mass  of  tissues  of  greater  or  less 
size.  When  this  mass  is  killed  by  the  formation  of  a  sheet 
of  cork  on  its  inner  face  it  gradually  dries  up  and  ultimately 
breaks  away  in  the  form  of  a  scale  or  flake  (fig.  129).  Hark 
of  this  sort,  such  as  that  of  the  hickory,  sycamore,  or  apple, 


Fig.  129. — Part  of  a  transvn^  ■., ■<  iii.ii  <>f  the  bark  of  cinchona.  c,  layers  oi  <<>rk 
formed  by  a  transient  cork  cambium.  s,  thin-walled  tissues,  with  occasional  stone 
cells.  The  sheets  of  cork  cells  are  lines  of  weakness  along  which  the  flakes  of  bark 
split  off.     Magnified  665  diam. — After  Warnecke. 


is  known  as  scaly  bark.  In  other  trees  the  dead  outer  por- 
tions are  persistent,  and  are  only  gradually  worn  away  by 
the  action  of  the  weather.  Such  persistent  parts  become 
seamed  or  deeply  furrowed  lengthwise  by  the  increased  size 
of  the  stem  within  and  the  constant  drying  and  shrinking 
of  the  dead  parts.  Such  bark  is  called  furrowed  or  ridgy 
bark. 


THE   STEM.  113 

140.  Lenticels. — In  stems  in  which  the  generating  layer 
of  the  periderm  is  formed  from  the  epidermis  or  the  cortex 
adjacent  to  it,  the  cork  cells 
produced  show  certain  modi- 
fications at  points  correspond- 
ing to  the  stomata  of  the 
epidermis.  Here  the  cork 
cells  become  rounded  and 
loosened  from  one  another 
(figs.  130,  131).  The  epider- 
mis under  the  strain  ruptures  „  ,  , .    . 

1  Fir,.  130. — A  bit  of  a  transverse  section  of  the 

first  at  the  Stoma,  and   exposes       cortex  of  elder,  showing  a  very  young  stage 

1  in  the  formation  of  a  lenticel.    1  he  cortical 

this   powdery   mass    of   cells     c.el,!,s  imder  a  f0"1?  havf  divi4ed  tangen- 

1  »  tially  and  are  ionning  a  loose  tissue  which 

through     a     USUally     biconvex        >las   already  torn   apart   the    guard    cells 

0  '  (See  hg..  131.)     Magnified  120  diam. — After 

rift,   whose  shape    suggested     8tahl- 

for    the   structure   the  name  lenticel.     Lenticels  are  formed 

either  beneath  single  stomata,  or,  when  the  stomata  are  not 


^^k4oM 


Fig.  131. — Transverse  section  through  .1  mature  lenticel 
Compare  fig.  130.     Magnified  80  diam. 


uniformly  distributed,  beneath  the  clusters  of  stomata.  When 
the  generating  layer  of  cork  is  deep-seated  the  lenticels  pro- 
duced are  without  relation  to  the  position  of  the  stomata. 
141.  2.  The  formation  of  secondary  wood  and  bast.- 
The  position  of  the  internal  generating  layer  (the  stelar  cam- 
bium) is  not  subject  to  the  same  variations  as  the  external 


ii4 


PLANT   LIFE. 


one.  In  stems  of  the  few  monocotyledonous  plants  which 
undergo  secondary  increase  in  diameter,  the  internal  generat- 
ing layer  arises  from  the  pericycle.  Upon  division  the  inner 
segments,  chiefly,  differentiate,  and  from  them  arise  new- 
isolated  bundle  pairs  (in  which  the  xylem  bundle  surrounds 
the  phloem  bundle)  and  new  pith  (fig.  132). 


Fig.  132. — Portion  of  a  transverse  se<  lion  of  a  stem  ol  Dracaena,  in  process  of  secondary 
thickening.  <■,  epidermis;  I:,  periderm;  > .  cortex,  in  which  a  bundle-pair 4  is  passing 
out  to  a  leaf :  .1 .  stelar  i  ambium  ;  ;  .  g,  vas<  ular  bundles  ;  nt,  primary  pith  ;  tt,  see  on- 
dary  pith.  The  amount  of  secondary  thickening  is  shown  by  the  radial  arrangement 
of  cells  of  secondary  pith.     Magnified  about  50  diam. — After  Sachs. 

In  the  many  dicotyledons  whose  stems  increase  in  diam- 
eter, the  stelar  cambium  arises  between  the  xylem  and  the 
phloem  bundles  of  each  pair,  and  extends  across  the  pith 
rays  which   intervene,  thus  forming  a  complete  zone  nearly 


THE    STEM 


115 


concentric  with  the  surface  of  the  stem  (figs.  120,  124,  133^). 
As  its  cells  divide,  sometimes  their  inner,  sometimes  their 
outer  segments  differentiate  into  the  tissues  which  they  then 


Fig.  133. — Diagrams  of  transverse  sections  of  stems  illustrating  modes  of  secondary 
thickening.  In  all  c,  cortex;  in,  endodermis ;  />,  pencycle  ;  ///',  primary  phloem ; 
ph.'  ,  secondary  phloem;  cb,  stelar  cambium;  .1 ',  primary  xylem;  x",  "secondary 
xylem  ;  >',  primary  pith  rays;  r",  secondary  pith  rays.— After  Van  Tieghem. 

adjoin.  Inside  the  generating  layer  between  the  bundles 
there  arises,  therefore,  secondary  xylem  which  becomes 
wood  ;  outside  it,  secondary  phloem,  or  bast.  Each  bundle 
is  thus  increased  in  its  radial  dimension  (fig.   124  ). 

142.  Pith  rays. — The  generating  layer  in  the  pith  rays 
arises  from  the  pericycle  or  from  some  part  more  deep- 
seated,  but  in  any  case  it  connects  directly  with  the  generat- 
ing layer  between  the  adjacent  bundles  (fig.  124).  In  this 
portion  of  the  generating  layer  two  distinct  modes  of  develop- 
ment are  to  be  observed  :  either  the  tissues  produced  by  the 
division  of  the  cells  differentiate  into  pith  tissue  (B,  fig.  133), 
or  they  form  secondary  wood  and  hast  corcsponding  to  that 
produced  between  the  adjacent  bundles.  In  the  latter  case, 
therefore,  a  complete  /one  or  ring  of  secondary  wood  and 
bast  is  formed,  so  that  the  pith  occupies  the  center.  Upon 
the  ring  of  secondary  wood  thus  produced  the  primary  wood 
bundle  projects  into  the  pith,  and  upon  the  ring  of  secon- 
dary bast   the   primary  bast   bundle   projects   into   the  rortex 

(C,  fig.  133). 


I  l6  PLANT  LIFE. 

Intermediate  between  these  two  methods,  it  is  common  to 
have  new  bundles  produced  by  the  differentiation  of  the 
secondary  tissues  formed  in  the  pith  rays,  these  bundles 
remaining  separated  by  pith  rays.  In  this  case  a  xylem 
bundle  is  usually  first  formed,  followed  shortly  by  a  phloem 
bundle  outside  (Z>,  fig.  133). 

The  secondary  bundles  thus  formed  can,  of  course,  have 
no  connection  with  those  which  enter  the  leaves.  In  this 
they  differ  from  the  primary  bundles,  branches  from  which 
enter  each  leaf.      (See  •[  163.) 

143.  Annual  rings. — If  the  stem  is  perennial,  year  after 
year  the  stelar  cambium  resumes  its  growth,  adding  layer 
after  layer  to  the  secondary  wood  and  bast.  Thus  most  trees 
have  their  shaft-like  trunks  formed.  The  generating  layer 
forms  a  line  of  weakness,  especially  when  dividing  rapidly, 
and  the  parts  outside  separate  readily  from  the  wood.  They 
constitute  the  bark. 

144.  3.  The  bark. — As  has  been  already  shown,  the 
outer  part  of  the  bark  consists  of  the  dead,  dry,  shriveled 
tissues  of  the  periderm  lying  outside  the  cork  cambium.  The 
inner  portions  of  the  bark  are  composed  of  the  tissues  which 
lie  between  the  cork  cambium  and  stelar  cambium.  This 
inner  part  contains  a  greater  amount  of  water  than  the  outer, 
and  always  some  living  tissues.  It  may  consist  of  a  part  of 
the  cortex  (depending  upon  the  place  of  origin  of  the  peri- 
derm), the  pericycle,  and  the  primary  and  secondary  bast. 
As  the  tree  grows  older,  the  secondary  generating  layers  of 
the  periderm  invade  the  cortex  and  the  bast,  until,  with 
weathering,  the  bark  may  come  to  consist  wholly  of  secondary 
bast.  It  attains  considerable  thickness  only  when  the  loss 
from  this  cause  is  slow. 


CHAPTER  X. 

THE     LEAVES. 

145.  Primary  leaves. — Leaves  are  distinguishable  into 
primary  and  secondary.  The  primary  leaves  arise  directly 
from  the  first  cells  produced  by  division  of  the  egg.  In  the 
fernworts  two  of  the  octants  into  which  the  egg  divides 
produce  the  primary  leaf.  This  is  entirely  unlike  the  secondary 
leaves,  which  arise  upon  the  sides  of  the  stem.  In  seed 
plants,  one,  two,  or  more  leaves  develop  as  members  of  the 
embryo,  only  a  I'ew  plants  (and  those  probably  degenerate  in 
this  respect)  not  forming  leaves  before  the  embryo  enters  its 
resting  stage. 

The  primary  leaves  of  seed  plants  are  called  cotyledons 
(figs.  134,  135).  They  are  usually  transient,  and  not  rarely 
so  distorted  by  acting  as  storage  places  for  reserve  food  that 
they  do  not  function  as  foliage  leaves  at  all.  In  extreme 
cases  of  this  kind  they  remain  in  the  seed  coats  when  the 
embryo  resumes  its  growth,  as  in  pea  and  oak. 

146.  Secondary  leaves  are  generally  numerous  and  much 
more  conspicuous.  It  is  these  which  are  usually  meant  by 
"  leaves,"  unless  primary  leaves  are  specially  named. 

147.  Development. — If  the  apex  of  the  shoot  is  examined, 
its  progressive  differentiation  into  stem  and  leaves  can  be 
observed.  Upon  the  sides  of  the  growing  point  swellings  of 
various  size  appear,  the  smallest  being  nearest  the  apex  (fig. 
95).  These  swellings  are  the  fundaments  of  the  leaves,  into 
which  they  become  transformed  by  further  development. 
Similar  swellings  appear  later  just  above  the  leaf  fundaments, 


PLANT  LIFE. 


which  are  at  first  not  distinguishable  from  them,  except  by 
position  (fig.  96).  These  become  the  branches.  Both  leaf 
and  branch  have  their  origin  usually  in  the  outer  layers  of  the 
shoot,  and  can  only  be  distinguished  by  the  later  course  of 
development.  The  growth  of  the  branch  is  commonly 
indefinite,   while  that  of  the  leaf  is  generally  limited  ;    the 


Fir..  134.  Fig.  .35. 

Fig.  134      A  seedling  oJ  wheat,  with  grain  still  attached  cut  through  lengthwise,  showing 

the  single   inim.iry  li.it  with   its  back  applied  to  the  store  ot   reserve  food  in  the  grain 
(the  shaded  part).    The  tirst  two  secondary  leaves  are  also  developing,  and  the  primary 
root  has  extended.     Magnified  4  diani      Alter  Kernel 
Fr<;.  135.— Seedlings,  showing  primary  leaves.     A,  a  fir  (.  Hies  orientalis);  />,  the  dog- 
rose;  C,  a  morning-glory.     Naturafsize. — After  Kerner. 

branch  usually  develops  leaves  and  often  buds  as  lateral  out- 
growths, while  the  leaf  rarely  forms  buds  normally  ;  the  axis 
of  the  branch  is  generally  radial,  like  the  parent  axis,  while 
the  leaf  is  generally  flattened  and  dorsiventral.  In  most  cases, 
also,  the  leaf  subtends  the  branch,  both  leaf  and  branch 
mark  those  points  of  the  stem  known  as  the  nodes. 


THE    LEA  VES.  I  1 9 

148.  Arrangement. — Leaves  appear  in  regular  succession 
upon  the  stem,  the  youngest  being  nearest  the  apex.  Their 
distribution  along  the  sides  of  the  stem,  though  extremely 
various,  may  be  reduced  to  two  main  types.  Either  (i)  the 
leaves  are  formed  singly  at  the  nodes,  or  (2)  more  than  one 
leaf  occurs  at  each  node.  When  the  leaves  are  single,  succes- 
sive leaves  may  stand  upon  exactly  opposite  sides  of  the  stem, 
so  that  the  third  leaf,  counting  from  below  upwards,  stands 
over  the  first ;  or  the  fourth  leaf  may  stand  over  the  first ;  or 
the  sixth  over  the  first,  and  so  on.  A  transverse  section  of  a 
bud  shows  the  mode  of  arrangement,  and  a  study  of  such 
sections  makes  it  evident  that  each  leaf  appears  in  the  widest 
space  between  the  two  preceding  leaves,  i.e.,  where  it 
encounters  the  least  resistance.  That  this  is  the  determining 
factor  is  shown  by  the  fact  that  the  order  of  arrangement  may 
be  artificially  altered  by  pressure  or  distortion  of  the  bud. 
When  two  or  more  leaves  occur  at  each  node,  the  members 
of  successive  circles  ordinarily  alternate  with  each  other. 
This  alternation  is  due  to  the  same  cause. 

149.  Form. — Leaves  show  a  great  variety  of  form  and 
structure.  Even  upon  the  same  plant  leaves  of  various  forms 
occur.  The  primary  leaves  are  usually  different  from  the 
secondary  leaves,  both  in  form  and  size.  The  most  abundant 
form  of  secondary  leaves  is  foliage  leaves.  These  may  be 
very  simple,  as  the  "  needles  "  of  the  pines,  or  differentiated 
more  completely,  as  in  the  deciduous  trees.  The  mature  form 
of  the  complex  foliage  leaf  is  frequently  not  attained  until 
several  nodes  above  the  point  at  which  the  primary  leaves 
arise;  and,  if  only  one  or  two  leaves  are  produced  each 
season,  as  in  many  ferns,  the  mature  form  may  not  appear  lor 
several  years. 

150.  Foliage  leaves. — A  well-developed  foliage  leaf  may 
usually  be  divided  into  two  equal  parts  by  a  plane  passing 
through    its  base   and   the   axis  of  the   stem   to   which    it   is 


120 


PLANT  LIFE. 


attached,  i.e.,  it  is  bilateral.     Moreover,  the  upper  and  under 

surfaces  are  usually  different,  i.e.,  it 

is  dorsiventral.      It  has  three  parts, 

the  base,  the  stalk,  the  blade  (fig. 

136).      The     leaf    base     is    always 

present,  but  either  the  leaf  stalk  or 

the  leaf  blade  or  both  maybe  absent. 

The  leaf  blade  is  ordinarily  winged  ; 

indeed  it  is  for  this  reason   that   il 

W-i 


Fig.  136.  Fig.  137. 

Fir,.  136.— Leaf  of   Ranunculus   Ficaria.     /-,  leaf  base;   /.petiole,  or  leaf  stalk;  /, 

lamina  or  leaf  blade.     Natural  size. — After  Prantl. 
Fig.  137. — A  leaf  of  a  grass,  with  part  of  stem  to  which  it  is  attached,     s,  sheath  (leaf 

base)attached  all  around  node  k  of  the  stem  //,  /;  ;  /,  blade  ;  /,  the  ligule,  an  outgrowth 

from  the  surface.     Natural  size. — After  Frank. 

received  the  name  "  blade."      Either  the  stalk  or  the  base  or 
both  may  also  be  winged. 

151.  1.  The  leaf  base. — The  leaf  base  is  generally  en- 
larged so  as  to  form  a  sort  of  cushion  by  which  it  is  attached 
to  the  stem.  When  a  broad  base  is  attached  over  a  consider- 
able arc  of  the  circumference  of  the  stem,  so  that  it  encircles 
it  more  or  less,  the  base  is  said  to  be  sheathing  (fig.  136). 
In  grasses,  for  example,  the  leaf  base  is  attached  over  the 
entire  circumference  of  the  stem,  and  enwraps  it  completely 
for  a  considerable  distance  above  the  node  (fig.  137). 


THE    LEAVES. 


121 


152.  Stipules. — The  leaf  base  frequently  branches.  These 
branches,  commonly  two  in  Dumber,  arc  called  stipules  (fig. 
138).      They  vary  from   slender,  awl -shaped  bodies  to   flat- 


Fir,.  138.— A  growing  shoot  of  a  thorn  (( 'rateegus  punctata),  n,  leaves  developed  as 
bud  scales  which  protected  the  parts  above  when  in  the  bud;  .V,  stipules.  Natural 
size. — After  Reinke. 


tened  and  leafdike  ones.  The  stipules  may  remain  attached 
to  the  base  throughout  the  life  of  the  leaf,  or  may  fall  away 
early.  Usually  the  two  are  separate,  but  they  may  be  united 
with  the  leaf  base  itself,  forming  wings  for  it,  as  in  roses 
(fig.  139),  or  they  may  be  united  with  one  another  so  as  to 
form  a  sort  of  sheath  encircling  the  stem  (fig.  140).  When 
the  leaf  base  is  winged,  the  wings  extend  downward  as  lobes 
more  or  less  encircling  the  stem.  In  many  cases  the  leaf  is 
said  to  be  clasping  (fig.  141  ).  These  lobes  may  even  unite 
on  the  other  side  of  the  stem,  so  that  the  stem  seems  to 
penetrate  the  base  of  the  blade.  (See  fig.  142.)  When  two 
leaves  occur  at  the  same  node,  corresponding  lobes  of  the 


PLANT   LIFE 


leaf  bases  may  unite,  so  that  the  stem  seems  to  pass  through 
the  center  of  a  leaf  which  extends  equally  on  each  side  of 
it.      (See  fig.  143.) 


Fig.  139—  A  young  flowering  shoot  of  dog-rose,  showing  various  forms  of  leaves  and 

transition  from  one  to  the  other.     «'-«*,  scale  leaves;  Z1-/3,  foliage  leaves;  A'-A*, 

-    hracts  ;    the  flower  leaves  not  clearly  shown.    The  scale  leaf,  «',  shows  a  leaf  base, 

winged  by  stipules  b,  with  only  a  trace  of  stalk  and  blade,;.    Trace  these  parts  into 

foliage  leaves,  where  the  blade  becomes  compound,  and  subsequent  reduction  through 
the  series  oi  bracts.      Natural  size.  — Alter  I.uerssen. 

153.  2.  The  leaf  stalk.— The  leaf  stalk  is  also  known 
as  the  petiole.  Its  form  is  more  or  less  cylindrical,  usually 
with  a  groove  or  channel  upon  the  upper  side.  Sometimes 
the  petiole  is  flattened  in  a  vertical  plane,  a.s  in  aspen  poplars. 


THE   LEAVES. 


23 


When  this  flattening  is  extensive,  so  that  the  petiole  becomes 
thin  and  leaf-like  and  the  blade  is  wanting,  it  functions  as  a 
foliage  leaf  (fig.  144).  Not  infrequent- 
ly, the  petiole  is  winged,  as  in  the  orange. 
It  may  be  entirely  wanting,  in  which 
case  the  blade  arises  directly  from  the 
base,  as  in   most   grasses 

(fig-   137). 

154.  3.  The  leaf 
blade. — To  this  part  of 
the  leaf  the  word  ' '  leaf ' ' 
itself  is  frequently  ap- 
plied. In  general,  the 
:he  leaf  blade  is  so  broadly 
winged  as  to  be  thin  and 

clasping   base.   flat  .     but     ^     gradations 


she. uli 


forming 


Potygvnu 

above  the  sheathing  leaf  base    . 
cut-off  leaf  f:    cc,   the  stem;    ca,   an    axillary 
shoot.     Natural  size. — Alter  Frank. 
FlG.    141.— Leaf  of    Tklaspi 
Natural  size. — After  Prantl 


Fig.  142.  Fir..  143. 

Fig.  142. — Shoot  of  Uvularia,  showing  perfoliate  leaves  below.     About  half  natural 
size— After  Cray. 

Fig.   143. — A  shoot  of  wild  honeysuckle,  showing  upper  leaves  connate-perfoliate. 
About  half  natural  size.— After  ( Iray 


124  PLANT  LIFE. 

exist  between  such  forms  and  those  that  are   much  folded  or 
crumpled,  thick  and  fleshy,  oi  even  cylindrical. 


Fig.  144.— A  shoot  of  Acacia,  showing  at  a  a  twice-branched  (compound)  leal  with 
roundish  petiole  ;  at  6,  a  similar  leaf  with  flattened  blade-like  petiole  ;  at  c,  phyllodia, 
i.e.,  blade-like  petioles  without  true  blades.    About  half  natural  size  (?). — After  Frank. 

If  a  thin  blade  be  held  between  the  eve  and  the  light,  two 
parts  become  evident :  (i )  a  green  tissue  (mesophyll),  more 
or  less  opaque  ;  and  (2)  translucent  "nerves"  or  "  veins."  * 
The  larger  of  these,  usually  called  the  "  ribs,"  *  frequently 
form  ridges  upon  the  under  surface.")" 

155.  Branching. — The  outline  of  the  blade  is  extremely 
various.  It  is  dependent  upon  the  character  and  extent  of 
its  branching,  which  may  be  either  slight  or  extensive. 
Slight    branching  gives  rise   to  teeth  of  various  forms  (fig. 

*  These  words  must  not  be  thought  to  indicate  any  resemblance  in  func- 
tion to  the  same  parts  in  animals,  but  only  similarity  of  position  or  ap- 
pearance. 

f  For  further  account  of  structure  see  ^[  168. 


THE   LEAVES. 


125 


145).      More  profound  branching  is  evident 'in  divided  or 
parted  leaves  (fig.  146).      In 
some    blades    the  branching 
is  so  extensive  and  complete 


Fig.  146. 
) ,  leaf  with  crenate  edge  ;  />',  leaf  with 


ARC 
Fig.  145- 
Fig.  145.— Diagrams  of  slight  leaf  branching 

dentate  edge  ;   C,  leaf  with  serrate  edge. — After  Bessey 
Fit;.  146. — Leaf  of  A morphophallus,  showing  sympodial  branching.     Th 
lateral  axes  are  numbered  in  order.    The  extent  of  branching  makes  the  blade  divided. 
Reduced. — After  Sachs. 

that  the  green  tissue  no  longer  fills  the  intervals  between  the 
larger  ribs,  but  the  blade  is  made  up  of  a  series  of  independ- 
ent portions  united  to  a  common  stalk.  Each  ultimate 
branch  of  the  blade  is  known  as  a  leaflet.  Blades  in  which 
the  green  tissue  is  continuous,  even  though  deeply  divided, 
are  called  simple  leases.  (See  figs.  136,  138,  141,  142,  145, 
146.  )  Those  which  are  segmented  into  leaflets  are  called 
compound  leaves.      (See  figs.  139,  144,  147,  148,  141).) 

156.  Venation. — The  mode  of  branching  of  the  blade  is 
indicated  by  the  main  ribs  which  occupy  the  axes  of  growth. 
(See  ^1  169.)  Study  of  distribution  of  the  ribs  and  veins  of 
the  blade,  that  is,  of  its  venation  or  nervation,  shows  that 
monopodial  branching  (*T  93)  is  the  common  mode,  sympo- 
dial branching  occurring  rarely  (fig.  146).  The  arrangement 
of  the  larger  ribs  may  be  reduced  to  two  main  types.*     (1) 


*  Compare  mode  of  branching  of  shoot,  "   i".;. 


126 


PLANT  LIFE. 


There  may  be  a  main  rib,  from  whose  flanks  arise  at  regular 
intervals  a  series  of  lateral  branches  which  may  themselves 


Fig.  148.  Fig.  149. 

Fig.  147.— A  palmately  branched  (compound)  leaf  of  horse  chestnut.     About  one-fifth 

natural  size.— After  Bessey. 
I'ii..  148. — A  palmately  branched  (compound)  leaf. —  After  ISessey. 
FlG.    Mi).— Leaflets   of    maidenhair   fern     showing   dichotomous    branching  of  veinlets, 

which  end  free.     Natural  size. — After  Ettingshausen. 

again  be  branched  in  various  ways.  Such  a  leaf  is  said  to  be 
pinnaiely  veined  (figs.  138,  151,  153).  Or  (2)  from  the  top 
of  the  petiole  several  large  ribs  of  almost  equal  strength  may 
be  given  off.  Such  venation  is  palmate  (figs.  150,  152). 
These  may  be  parallel  (fig.  150)  or  radiate  (fig.  152). 

The  distribution  of  the  small  veins  or  nerves  shows  three 
types.  They  may  either  (1)  connect  with  each  other  so  as 
to  form  an  irregular  meshed  network  (fig.  151);  or,  (2)  leav- 
ing  a  rib  nearly  at  right  angles,  they  may  run  parallel  with 
ea<  h  Other  to  join  another  large  vein  ;   or  (3)  they  may  leave 


THE   LEAVES.  1 27 

the  large  vein  and  end  free  (fig.  149).  In  the  first  type  the 
finest  branches  of  the  veins,  too  delicate  to  be  seen  without 
the  microscope,  often  end  free  in  the  meshes  formed  by  the 
next  larger  branches  (fig.  164).     Near  the  margin  of  a  blade 


Fig.  150.  Fig.  151. 

Fig.  150— Parallel  venation  of  leaf  of  Polygonatum  latifolium.  Natural  size. — 
After  Ettingshausen. 

Fig.  151. — Pinnately  netted  venation  of  leaf  of  a  willow.  Natural  size.— After  Ettings- 
hausen. 

the  larger  veins  are  often  so  connected  with  each  other  as  to 
form  one  or  more  series  of  arches  whose  convex  side  is 
directed  toward  the  margin.  These  forma  sort  of  selvedge 
and  protect  the  leaf  against  tearing  (fig.  153). 


128 


PLANT   LIFE. 


157.  Special  forms. — Foliage  leaves  may  be  modified  to 
serve  special  purposes  without  wholly  losing  their  function  as 


Fig.  152. — Palmately  veined  and  branched  leaf  of  Norway  maple.     About  half  natural 
size. — After  Kerner. 

foliage.     For  example,  the  petiole  may  be  made  sensitive  to 

contact  and  adapted  to  wrap  about  slender   objects,  like  a 

tendril,  as  in  clematis  and  j^fs,         *t 

nasturtium  (fig.  154).  Such 

plants  are  called  leaf-climb-  — '  v 

ers. 


Fig.  154. 

Fir..  153 .— Pinnately  veined  leaf  of  buckthorn,  with  looped  ribs  forming  a  selvedge. 

After  Kerner. 
Fig.  154.— Portion  of  a  plant  of  the  dwarf  garden-nasturtium  {Trofiaolum  minus). 

The  long  petiole  a,  ,*,  ,1   of  the  leaf  /  is  sensitive  to  contact  and  has  coiled  about 
the  support  and  its  own  stein,  st.     ~,  axillary  branch.     Natural  size.— After  Sachs. 


THE   LEA  VES. 


29 


Some  plants  develop  their  leaves  into  the  form  of  sacs  or 
pitchers.  These  ordinarily  represent  the  black-  of  the  leaf, 
and  are  more  or  less  urn-  or  trumpet-shaped.  They  may  be 
either    without    petiole,    as    in     Sarracenia    (fig.     155);     or 


A     ••-;- 


Fig.   155. — Pitcher-plant  {Sarracenia  purpurea).      Leaf  above   A   cut  off  to  show 
trumpet  form.     One-third  natural  size. — After  Gray. 


petioled,  as  in  Utricularia  |  figs.  383,  384)  ;  or  the  petiole 
may  be  winged  to  serve  for  foliage,  as  in  Nepenthes  (  fig. 
382).  A  few  plants  have  their  leaves  modified  so  as  to  serve 
as  traps,  which,  by  their  sudden  movements,  capture  small 
animals  (figs.  386,  387,  388). 

But  generally  the  foliage  function  is  subordinated  to  the 
other  work,  and  the  leaf  takes  on  peculiar  forms,  the  more 
important  of  which  are  as  follows  : 


i3o 


PLANT   LIFE. 


158.  (i)  Tendrils. — The  leaf  blade  alone,  or  some  of  its 
branches,  or  the  petiole  and  blade,  may  develop  as  a  cylin- 
drical body,  without  wings  and  sensi-  -  ,, 
live,  known  as  a  tendril.  In  the  pea,  ^^  I^U* 
the  stipules  become  very  large,  and 
take  the  function  of  the  reduced  blade 
(fig.  156).  In  other  plants  the  base 
may  be  broadly  winged  for  the  same 
purpose. 


Fig.  ,56. 

Fig.  156.— Portion  of  shoot  of  pea,  with  a  pmnatcly  compound  leaf  whose  upper  leaflets 

are    modified    into   tendrils    and   the   stipules   greatly   developed   to   serve   as   foliage. 
About  half  natural  size.— After  Frank. 
Fir..  157. — Piece  of  the  stem  of  locust  {Robinia  Pseudacacia),  showing  stipules  in  the 
form  of  thorns.     Natural  size. — After  Kerner. 

159.  (2)  Thorns. —  The  leaves  may  develop  into  slender 
conical  and  sharp-pointed  thorns  or  spines,  either  branched 
or  unbranched  (fig.  390).  Sometimes  the  stipules  alone 
become  thorns,  as  in  locust  and  acacia  (fig.  157).  Neither 
tendrils  nor  thorns  can  be  distinguished  structurally  from 
similar  forms  of  the  shoot. 

160.  (3)  Scales.  —  In  buds,  on  underground  stems  and 
on  various  parts  of  the  aerial  stem,  are  found  small,  scale-like 
leaves  of  various  shapes  (figs.  101,  102,  105,  109,  138,  139, 


THE   LEAVES.  13 ' 

358).  These  scales  may  represent  the  sheathing  base  only  ; 
they  may  be  the  base  with  the  stipules  (fig.  139);  or  they 
may  represent  the  leaf  base  and  the  blade.  The  petiole  in 
all  cases  is  wanting.  In  addition  to  the  modification  of 
form,  scales,  especially  those  that  are  protective,  have  their 
tissues  firmer  and  more  resistant  to  cold  and  unfavorable 
external  conditions.  Not  infrequently  the  scales  are  covered 
with  secreting  hairs,  or  possess  glands  sunk  beneath  their 
surfaces,  whose  function  is  to  produce  and  excrete  resins  and 
similar  materials.  The  inner  protective  scales  of  buds  (fig. 
98)  are  often  covered  with  an  abundant  coating  of  woolly 
hairs,  which  serve  to  prevent  rapid  change  of  temperature  in 
the  interior  of  the  bud. 

161.  (4)  Flower  leaves  and  bracts. — -On  certain  parts  of 
the  stem,  leaves  are  commonly  profoundly  modified  to  carry 
the  spore  cases.  They  are  called  sporophylls  (c,  si,  fig.  104). 
(See  ^[  329.)  Adjacent  to  these  are  others  which  may  be 
highly  colored  and  adapted  in  form  to  protect  the  sporo- 
phylls, and  to  facilitate  the  visits  of  insects  (s,  p,  fig.  104). 
A  shoot  whose  leaves  are  thus  clustered  and  specialized  con- 
stitutes a  "  flower."  The  leaves  adjacent  to  the  flower  leaves 
are  also  more  or  less  modified  in  form  and  reduced  in  size. 
They  are  called  bracts  (//  •>  2>  3.  fig.   139).      (See  also  ^[  359.) 

162.  (5)  Storage  leaves. — Other  leaves  are  utilized  for 
purposes  of  storage.  For  this  purpose  the  ribs  are  reduced  in 
number  and  size,  while  the  softer  tissues  of  the  leaf  are  often 
enormously  developed,  and  serve  as  the  receptacles  of  the 
reserve  food.  The  primary  leaves  of  the  seed  plants  (coty- 
ledons) are  often  much  distorted  by  the  deposit  in  them  of 
reserve  food  for  the  embryo.  When  such  leaves  possess 
sheathing  bases  the  structure  resulting  from  the  union  of  a 
number  of  such  leaves  upon  a  short  axis  is  called  a  bulb. 
(See  also  ^f  109.)  The  leaves  of  buds  are  sometimes  thick: 
ened  by  the  deposit  of  food    material,  and   when   such   buds 


132  PLANT  LIFE. 

loosen  from  the  plant  they  may  produce  a  new  plant,  as  in 
the  tiger-lily  (see  ^[  361-364).  Both  base  and  blade  may  be 
used  for  storage,  as  in  the  century-plant  j  or  the  entire  leaf 
may  serve  the  same  purpose,  as  in  the  cultivated  cabbage. 

163.  Structure. — Three  regions  in  each  part  may  be  dis- 
tinguished, as  in  the  root  and  stem  :  (1)  the  epidermis  ;  (2) 
the  cortex  ;  both  continuous  with  that  of  the  stem  ;  (3)  the 
Steles,  continuous  with  those  of  the  stem  when  the  latter 
contains  several  steles,  or  branches  of  it  when  the  stem  con- 
tains a  single  stele. 

164.  (a)  The  petiole. — The  structure  of  the  petiole  agrees 
in  all  essentials  with  that  of  the  stem  (see  %  124  {{.).  The 
epidermis  forms  the  outer  surface,  frequently  with  hairs  or 
emergences  (see  ^[128,  129).  The  cortex  consists  of 
rounded  or  cylindrical  thin-walled  cells,  the  outer  layers 
containing  chlorophyll,  and  frequently  with  angles  much 
thickened  for  strength.  Mechanical  tissues  forming  strands 
or  bands  are  also  frequently  present  in  the  cortex.  In  water 
plants,  e.g.,  in  water-lilies,  large  intercellular  chambers, 
often  forming  extensive  canals,  arc  present.  There  may  be 
a  single  stele,  surrounded  by  an  endodermis  and  containing 
several  or  many  vascular  bundles  (B,  fig.  158);  or  there  may 

A  />• 


Fig.  158. — Diagrams   of  transverse  sections  of  petioles  shoving  two   most  common 

structures.  A,  petiole  with  several  steles,  /.'.  petiole  with  one  stele,  containing  a 
number  of  bundle  pairs.  ,.  cortex;  en,  endodermis;  ///,  phloem;  jr,  xylem ; 
in.  pith  ;  '  ,  pith  rays  I  he  letters  .1 ,  B  stand  on  the  upper  or  ventral  side  of  petiole. 
— After  Van  Tieghem. 

be  several  steles,  each  surrounded  by  a  special   endodermis 
and  consisting  of  little  more  than  a  pair  of  vascular  bundles 


THE    LEAVES. 


133 


(A,  fig.  158).  In  transverse  section  the  vascular  bundles 
are  variously  placed,  being  irregularly  scattered,  or  disposed 
in  one  or  several  groups.  The  single  group  is  most  common, 
with  the  paired  bundles  placed  so  as  to  form  a  crescent,  or 
even  a  complete  ring,  which  is  flattened  above  or  triangular. 
The  largest  pair  is  generally  median  and  dorsal  (fig.  158), 
with  smaller  ones  right  and  left. 

165.  (b)  The  blade. — In  broad  leaves,  the  epidermis  of 
the  blade  is  made  up  of  tabular  cells,  often  with  wavy  lateral 
walls  (fig.   159).      In   narrow  leaves   the   epidermal  cells  are 


Fig.  159. — Surface  view  of  epidermis  from  under  side  of  leaf  of  bracken  fern  {/'let  is), 
showing  wavy  cells,  except  over  veins,  v,  where  they  are  elongated,  st,  stomata. 
The  dot  in  each  cell  represents  the  nucleus.  Highly  magnified. — After  Sedgwick  and 
Wilson. 

longer  than  wide  (fig.  160).  Over  the  veins  the  (ells  are 
elongated  parallel  with  the  vein.  The  epidermal  cells  are 
generally  free  from  chloroplasts.  The  epidermis  usually 
consists  of  one  layer,  but  in  some  plants  becomes  several 
layered,  either  to  serve  as  additional  protection  against  eva- 
poration or  for  use  as  a  water-storing  tissue.       (  See  •    441.  ) 


'34 


PLANT   LlfE. 


Hairs  of  many  sorts,  plain,  stinging  and  glandular,  and 
of  various  sizes,  arise  from  the  epidermis  (figs.  361-365). 
They  are  essentially  like  similar  structures  on  the  stem  (figs. 
113,  114). 

166.  Stomata. — Numerous  intercellular  spaces  bounded 
by  a  pair  of  specialized  cells,  called  guard  cells,   penetrate 


Fig.  160.— Surface  '.iew  of  epidermis  from  the  leaf  of  oat,  showing  elongated  cells  (more 
elongated  over  vein,  >i,  >:)  and  stomata  arranged  in  lines.  Moderately  magnified. — 
After  Frank. 

Fig.  161. — Perspective  view  of  a  stoma  from  the  under  epidermis  of  the  beet  leaf,  show- 
ing the  sloping  sides  of  the  slit,  the  crescentic  guard  cells  with  chloroplasts.  Highly 
magnified.— After  Frank. 

Fig.  162.— Sections  through  stomata  of  beet  at  right  angles  to  their  length.  The  upper 
figure  shows  the  stoma  open  ;  the  lower  closed.  The  black  line  represents  the  primary 
wall,  to  which  additional  material,  especially  in  the  guard  cells,  has  been  added. 
These  thickenings  serve  by  their  elasticity  to  close  the  stoma.  Opening  is  dm-  to 
turgor  "i  the  guard  cells  The  chloroplasts  and  granular  protoplasm  are  shown. 
Highly  magnified.     Alter  Frank. 

the  epidermis.  The  whole  apparatus  is  called  a  stoma  (s/, 
fig.  159,  160).  The  guard  cells  are  crescentic,  sometimes 
with  enlarged  ends  (fig.   160,  like  curved  dumb-bells   then), 


THE   LEAVES.  I  35 

and  arc  sensitive  to  various  external  conditions,  especially 
light,  so  as  to  control  the  size  of  the  slit-like  space  between 
them  by  changes  in  their  curvature  (fig.  162).  This  slit  is 
formed,  like  most  intercellular  spaces,  by  the  partial  splitting 
apart  of  the  cells.  It  communicates  with  extensive  intercel- 
lular spaces  in  the  interior. 

The  stomata  are  very  numerous.     In  different  plants,  in 


the  space  here  enclosed 


,  the  numbers  usually  vary 


from  4000  to  30,000,  sometimes,  however,  reaching  as  much 
as  60,000  to  70,000  in  the  olive  and  rape.  They  are  not 
equallyjlistrihuted  onJhe  two  sides  of  the  leaf.- being  usually 
more  numerous  j)n  the  under^sidej  where  there  arc  nmrc  in- 
ternal intercellular  spaces..  They  may  be  wanting  on  the 
upper  side,  as  in  lilac,  begonias,  and  oleander.  There  are 
no  stomata  on  submerged  leaves  nor  on  the  under  sides  of 
floating  leaves.  In  some  plants  they  are  found  in  clusters, 
in  others  uniformly  distributed. 

167.  Cortex. — -The  cortex  of  leaves  is  called  the  meso- 
phyll.  It  consists  of  thin-walled,  active  cells,  for  the  most 
part  richly  supplied  with  chloroplasts.  In  thick  leaves  the 
internal  cells  are  without  them.  In  some  leaves  the  cells  of 
the  mesophyll  are  nearly  uniform,  but  in  most  those  near  the 
upper  surface  are  more  elongated  and  close  set,  forming  one 
or  two  rows,  with  their  ends  outward,  while  cells  near  the 
lower  surface  are  irregular  in  form,  with  large  intercellular 
spans.  These  tissues  are  known  as  the  palisade  and  spongy 
parenchyma  (fig.  163). 

About  the  steles,  the  cortex  forms  the  usual  endodermis 
{gs,  fig.  163),  and  often  develops  along  the  larger  into  one 
or  two  strands  or  a  sheath  of  mechanical  tissues.  These 
tissues,  together  with  a  stele,  constitute  the  rib  or  vein,  often 
so  massive  as  to  project  beyond  the  other  parts  in  thin  leaves. 


136 


PLANT  LIFE, 


168.   Steles.-    The  steles  are  numerous  and  ramify  through 
the  blade.      Their  structure  is  essentially  as  described  for  the 


Fig.   163.— Diagrammatic  vertical  section  of  a  leaf, 
and  stomata  sp,  sfi.    Between  upper  and  lower  epid 


pidermis,  with  cuticle  c,  c, 
the  mesophyll,  with  cells 


ivii,  1 
abundantly  supplied  with  chloroplasts.  The  upper  row  of  elongated  cells  is  the  pali- 
sade parenchyma  ;  the  rest  form  the  spongy  parenchyma,  both  with  many  intercellular 
mmunicating  with  outside  air  through  stomata.  In  the  mesophyll  lies 
a  small  vein,  here  cut  across,  composed  of  a  ventral  xylern  bundle  v.  a  dorsal  phloem 
bundle  ,v,  surrounded  by  the  endodermis  .;,*.  and  the  pericyclc  (between  e  and  .!,•■»')■ 
After  Sachs. 


stem  (•]  127).  Each  of  the  smaller  consists  of  little  more 
than  a  single  pair  of  vascular  bundles.  The  xylem  bundles 
alone  form  the  last  branches  (fig.  164),  the  phloem  disappear- 
ing earlier.  The  larger  ribs  may  form  one  or  two  strands  or 
a  complete  sheath  of  mechanical  tissues  by  the  development 
of  the  pericycle,  and  the  bundles  proper  may  be  increased 
by  the  development  of  secondary  wood  and  bast.  (See 
■"   141. 


THE    LEAVES.  1 37 

169.   Growth.— The  growth  of  the  leaf  is  at  first  apical. 
In  fern-worts  its  tissues  are  produced   by  the  continued  divi- 


FiG.  i^. — A  few  meshes  of  the  finest  veins  of  a  leaf  of  A  nthyllis.  »i ,  main  vein  ;  />,  />, 
branches  ;  <;.  .;,  .;.  a  closed  mesh  ;  .  .  ends  of  the  finest  veins  within  the  mesh.  The 
drawing  shows  only  the  xylem  bundles  ;  the  phloem  bundles  accompanying  them  and 
the  mesophyll  cells  filling  the  meshes  are  not  shown.  Moderately  magnified. — After 
Sachs. 

sion  of  a  single  apical  cell,  and  the  further  division  of  each 
of  the  segments  so  produced  (/,  fig.  76).  The  branches  of 
such  leaves,  therefore,  arise  in  acropetal  succession.  In  most 
seed  plants,  instead  of  a  single  apical  cell,  there  is  a  cluster 
of  such  cells.  Growth  at  the  apex  often  ceases  early,  and  is 
replaced  by  growth  throughout  the  whole  extent  of  the  leaf. 
This  intercalary  growth  is  sometimes  localized  between  the 
fundament  of  leaf  base  and  blade,  producing  the  petiole 
when  one  is  formed.  In  elongated  leaves  without  distinct 
petiole,  as  in  grasses  and  many  other  monocotyledons,  a  zone 
of  growth  occupies  the  entire  base  of  the  blade.  By  the 
division  of  these  cells,  chiefly  at  right  angles  to  the  length 


i.SS 


PLANT   LIFE. 


of 


ith 


of  the  Made,  its  tissues  are  produced.  In  such  plants  apical 
growth  ceases  so  early  that  it  can 
be  observed  only  in  the  youngest 
stages. 

170.  Of  branched  leaves. — 
When  the  leaf  is  to  become  much 
branched,  two  or  more  new  growing- 
points  develop,  so  that  each  of  the 
branches  has  at  its  apex  a  growing- 
point  (fig.  166).  These  growing- 
points  may  arise  from  the  apical 
growing-point,  or  from  the  basal 
one,  or  sometimes  from  both.  The 
branches  will  appear  accordingly 
the  in  acropetal  or  basipetal  succession, 
the  or  even  in  both  as  they  do  in  the 
The  limits  of  the 
growing-point  are  even  more  in- 
definite than  in  the  stem.  The  cells  of  which  the  leaf  is 
composed  are  produced  very  rapidly,  and  at  a  very  early 
stage  division  ceases. 

171.  Wintering. — In  those  plants  which  live  from  year  to 
year,  producing  new  leaves  each  spring,  the  unfolding  of 
these  from  the  winter  buds  is  due  chiefly  to  the  enlargement 
of  cells  already  formed.  New  leaves  are  ordinarily  produced 
before  the  close  of  the  growing  season  preceding  that  in 
which  they  are  expanded,  and  are  protected  in  the  winter 
buds.  The  partly  developed  leaves  in  the  bud  may  be  flat, 
but  broad  leaves  are  commonly  folded  or  rolled  in  various 
ways. 

172.  Growth  limited. — The  growth  of  the  leaves  is  ordi- 
narily limited,  rarely  extending  over  a  single  season.  In  a  few 
ferns  and  coniferous  plants  the  leaves  continue  to  grow  for  a 
longer  time.      Indeed,  in  the  curious  Welwitschia  (fig.  167), 


Fir..  1^.5.  —  Ending  of  a  v« 
mesophyll  of  a  leaf,  t, 
spirally  thickened  cell 
xylem  ;  c,  c,  mesophyll  cells  win 

chioropiasts ;  a,  a,  cells  of  the  leaves  of  yarrow. 

endodermis.   Magnified  230  diam 
— After  Frank. 


THE   LEAVES. 


1 39 


the  basal  growth  of  a  single  pair  of  persistent  secondary 
leaves  is  continued  throughout  the  long  life  of  the  plant, 
while  the  tips  die  and  are  frayed  out. 

173.  Production  of  the  other  members. — Leaves  give  rise 
under  certain  conditions  to  roots  or  to  shoots.  The  number 
of  plants,  however,   in  which  this  occurs   is  comparatively 


FlG.  166. — Development  of  the  pinnately  compound  leaf  of  the  locust  {Robinia  Pseud- 
acacia).  .  I ,  young  stage,  snowing  on  one  flank  the  first  lateral  growing-point,;, 
which  is  to  produce  the  lowest  leaflet.  />',  an  older  stage  with  the  fifth  growing-point 
x  just  showing.  A  sixth  is  still  to  be  developed.  The  hairs  in  A  and  A' are  on  the 
back  (under  side)  of  the  leaf,  and  drop  off  early.  C*,  nearly  mature  leaf.  ./,  /■', 
magnified;  c,  about  i  natural  size.— After  Frank. 

limited.  Roots  arise  from  leaves  in  precisely  the  same  way 
as  lateral  roots  arise  from  stems  (•[  95),  that  is,  they  arc  en- 
dogenous in  their  origin,  and  develop  always  near  the  surface 
of  the  steles. 

When  a  leaf  produces  a  shoot,  it  is  from  the  epidermis  or 
from  the  green  tissue  underlying  it,  never  from  the  steles. 
Shoots  thus  arise  from  the  part  of  the  leaf  corresponding  to 
that  from  which  branches  arise  upon  the  parent  shoot. 

174.  Secondary  changes. — Leaves,  like  stems  and  roots, 
undergo  certain  secondary  changes,  hut  these  are  neither  so 


140  PLANT  11  IE. 

common  nor  so  extensive  as  in  the  other  two  members.  The 
formation  of  several  to  many  layers  of  cork  cells  upon  the 
surface  of  scale  leaves  is  not  uncommon.  Occasionally  simi- 
lar layers  of  cork  are  formed  upon  the  petioles  of  ordinal) 


Fig.  167. — Welwitschia  mirabilis,  a  coniferous  plant  of  Africa,  showing  two  leaves 
which  grow  at  base  and  continue  to  develop  throughout  the  many  years  which  the 
plant  lives.  The  tips  are  dead,  and  become  worn  and  frayed  by  winds.  .."j  natural 
size. — After  Hooker. 

foliage  leaves.  In  some  cases  the  large  vascular  bundles 
occupying  the  main  ribs  undergo  changes  similar  to  those  de- 
scribed for  the  bundles  of  the  stem  (*  141),  by  which  sec- 
ondary wood  and  bast  are  produced. 

175.  Leaf  fall. — One  of  the  secondary  changes  of  most 
importance  is  the  preparation  for  the  fall  of  the  leaf.  This  is 
made  by  the  formation  of  a  layer  of  secondary  meristem  across 
the  leaf  base  at  or  near  the  point  where  it  joins  the  stem. 
The  cells  at  this  point,  with  the  exception  of  those  constitut- 
ing the  vascular  bundles,  begin  a  series  of  divisions  at  right 
angles  to  the  axis.  A  transverse  plate  of  cells  is  thus  formed, 
some  of  which  cells  may  become  transformed  into  cork,  mak- 
ing a  line  of  weakness ;  or,  without  such  alteration,  the 
cells  may  round  themselves  off  by  loosening  along  a  definite 
line,  so  that  the  leaf  is  held  only  by  the  steles.     The  access 


THE  LEAVES.  Hr 

of  water  to  this  crevice,  and  its  freezing,  serve  to  rupture  the 

remaining  tissues,  and    thus  allow  the  leaf  to  fall   by  its  own 
weight,  or  to  be  torn  off  by  the  wind. 

The  scar  left  by  the  fall  of  the  leaf  is  protected  either  by 
the  cork  already  produced,  or  by  mere  drying  of  the  exposed 
tissues.  The  leaflets  of  compound  leaves  fall  in  like  manner. 
Sometimes  provision  for  the  leaf  fall  is  begun  as  early  as  June, 
as  in  the  Kentucky  coffee-tree.  In  other  plants  provision 
for  leaf-fall  is  begun  late  in  the  season,  and  in  some,  such  as 
the  oaks,  it  is  very  imperfect,  so  that  the  leaves  are  finally 
wrenched  off  by  winter  storms,  or  pushed  off  in  the  spring  by 
the  developing  buds  beneath  them. 


PART  II:   PHYSIOLOGY. 

CHAPTER    XI. 

INTRODUCTION. 

176.  Division  of  labor. — The  study  of  the  external  form 
and  internal  structure  of  plants  may  be  carried  on  as  well 
upon  dead  as  upon  living  material.  Even  the  observation  of 
the  various  stages  of  development  requires  only  the  examina- 
tion of  the  plant  as  it  exists  at  a  particular  moment.  But  the 
plant  may  also  be  studied  as  a  working  organism.  For  this 
purpose  living  material  is  indispensable.  The  work  which 
plants  do  and  by  which  they  are  distinguished  from  non- 
living bodies  is  extremely  varied,  and  the  more  complex  the 
plant  the  more  varied  it  is.  In  the  preceding  part  the  aim 
has  been  to  show  that  there  exists  great  variety  of  form,  and 
that  from  the  smaller  to  the  larger  plants  there  is  gradually 
increasing  complexity  by  differentiation  into  tissues  and 
members. 

Nutrition,  respiration,  growth,  movement,  and  reproduction 
are  all  executed  by  the  single  cell  of  the  simplest  plant. 
But  with  specialization  in  structure  there  occurs  division  of 
labor.  Each  kind  of  physiological  work  is  known  as  a 
function,  and  each  part  of  the  organism  which  does  a  par- 
ticular work  is  called  an  organ. 

177.  Physiology  and  ecology. — Physiology  proper  treats 
of  the  plant  at  work,  discussing  the  different  functions  and 

M3 


144  PLANT   LIFE. 

the  way  in  which  these  are  affected  by  external  forces.  In 
its  broadest  sense  it  also  treats  of  the  relation  of  the  plant  as 
a  whole  to  external  forces  and  to  other  living  beings,  both 
plants  and  animals.  But  it  is  convenient  to  separate  the 
latter  from  physiology  proper  as  ecology.*     (See  Part  IV.) 

The  study  of  physiology  proper  necessitates  methods  of 
controlling  these  external  forces,  carefully  planned  and  re- 
peated experiments,  and  cautious  inferences. 

The  study  of  ecology  requires  observation  in  the  field  of 
the  adaptations  of  plants  to  prevent  injury  by  unfavorable 
physical  conditions  and  the  attacks  of  other  beings,  and  to 
take  advantage  of  the  favorable  forces  and  beneficent  agents. 

178.  Chemical  and  physical  forces. — The  functions  of  a 
plant  may  be  divided  for  the  sake  of  convenience  into  nu- 
trition, respiration,  growth,  movement,  and  reproduction. 
These  are  largely  special  modes  of  chemical  and  physical 
action.  Nutrition  and  respiration,  for  example,  consist 
chiefly  of  a  series  of  chemical  changes  ;  while  movement  is 
mainly  a  result  of  physical  alterations  in  certain  organs. 
But  the  action  of  chemical  and  physical  forces  does  not  suffice 
at  present  to  explain  all  the  phenomena  of  the  living  plant. 
Moreover,  the  peculiar  manifestation  of  these  forces  which 
we  call  life  occurs  only  in  connection  with  the  substance 
which  we  call  protoplasm. 

179.  The  unit  of  function. — The  functions  performed  by 
the  entire  plant  are  necessarily  a  sum  of  the  functions  per- 
formed by  the  physiological  units  of  which  it  is  composed. 
As  the  unit  of  structure  is  the  plant  cell,  so  the  unit  of 
function  is  the  protoplasmic  body  of  that  cell.  Although 
only  a  portion  of  any  plant  is  composed  of  living  matter,  it 
is  to  that  living  matter  only  that  we  are  to  look  for  the  seat 
of  its  powers. 

*  Spelled  in  lexicons,  cecology,  but  best  usage  drops  the  o  ;  sometimes 
improperly  called  biology  or  plant  biology. 


INTRODUCTION.  145 

180.  The  fundamental  powers  of  protoplasm  arc  tour ;  it 
is  metabolic,  irritable,  contractile,  and  reproductive. 

181.  Metabolism. — Protoplasm  is  metabolic,  thai  is,  it  is 
capable  of  initiating  a  series  of  chemical  changes  in  itself  and 
in  substances  which  come  directly  under  its  influence.  These 
changes  are  of  two  kinds.  They  may  be  constructive,  i.e., 
they  may  build  up  complex  substances  out  of  simpler  ones, 
and  so  fit  them  for  use  in  repairing  the  waste  caused  by  the 
activity  of  the  protoplasm;  or  they  may  be  destructive,  i.e., 
they  may  break  down  complex  substances  into  simpler,  so 
setting  free  the  energy  necessary  for  the  work  of  the  pro- 
toplasm. The  substances  broken  down  may  be  repaired  in 
whole  or  in  part,  i.e.,  may  take  part  in  constructive  me- 
tabolism. Those  in  which  no  repair  occurs  often  undergo 
further  destructive  changes  by  which  they  become  converted 
into  materials  useless  to  the  plant,  and  to  be  gotten  rid  of. 
Metabolism,  therefore,  includes  all  the  chemical  changes  by 
which  food  is  either  manufactured  or  utilized,  and  by  which 
waste  materials  are  produced  and  eliminated. 

182.  Irritability. — Protoplasm  is  irritable,  that  is,  it 
exists  in  such  a  state  that  it  is  sensitive  to  external  influences, 
which  thereby  affect  the  various  functions  of  the  whole 
organism  By  reason  of  its  irritability,  it  may  even  transmit 
the  effects  of  an  external  stimulus  from  one  part  to  a  distant 
part.  Moreover,  it  is  capable  of  initiating  similar  changes 
without  the  action  of  any  observable  external  influences,  and 
is,  therefore,  not  only  irritable  but  automatic. 

183.  Contractility. — Protoplasm  is  contractile,  that  is,  it 
has  the  power  of  altering  its  form,  of  shortening  in  one 
direction  and  elongating  in  another,  by  virtue  of  inherent 
forces  whose  action  is  not  understood. 

184.  Reproduction.  —  Protoplasm  is  reproductive,  that  is, 
it  is  capable  of  so  directing  the  chemical  and  physical  forces 


I46  PLANT  LIFE. 

inherent  in  it  that  a  new  organism  similar  to  that  of  which  it 
forms  part  may  be  produced. 

185.  Adaptation.- -The  interrelation  of  these  powers, 
their  harmonious  coworking  and  their  variation  to  suit  the 
varying  conditions  of  the  surrounding  media  (air,  water,  soil, 
etc.),  result  in  the  proper  performance  of  all  the  functions  of 
the  plant.  By  means  of  these  powers  it  is  brought  into  re- 
lation to  the  world  about  it,  being  adapted  to  other  organisms 
in  whose  company  it  lives,  and  enabled  to  withstand  the 
adverse  conditions  by  which  it  is  frequently  threatened. 
Every  organism,  indeed,  must  adjust  itself  first  to  the  external 
physical  conditions,  and,  second,  to  other  organisms.  (See 
Part  IV.) 

186.  Physical  conditions  set  limits  upon  the  discharge  of 
its  functions.  Varying  amounts  of  light,  of  heat,  of  moisture, 
determine  more  or  less  rigidly  how  rapidly,  or  to  what  extent, 
each  function  may  be  discharged.  Every  function  of  the 
plant  is  adapted,  therefore,  to  an  upper  limit,  the  maximum, 
and  to  a  lower  limit,  the  minimum,  above  or  below  which 
the  performance  of  the  function  in  question  is  impossible. 
Between  these  limits  there  lies  some  point  at  which  it  pro- 
ceeds most  rapidly  and  effectively.  This  point  is  known  as 
the  optimum. 


CHAPTER    XII. 

THE  MAINTENANCE  OF  BODILY  FORM. 

Every  plant  is  capable  of  attaining  and  maintaining  a 
specific  form,  which  is  not  permanently  altered  by  the  direct 
action  of  external  forces,  and  is  dependent  upon  the  nature 
of  the  plant  itself. 

187.  Naked  cells. — If  the  plant  consists  of  a  single  mass 
of  naked  protoplasm,  it  may  assume  a  spherical  or  ovoid 
shape  (fig.  1 68).      In  attaining  this  form  the  physical  forces 


Fir..  iftS.—  Zoospores  of  various  Forms, 
cilia.  ./,  Botrydium ;  />',  Draf>ai 
Highly  magnified  .—After  Kerner. 


vimming  in  water  by  means  of  one  or  mo 
aldia;    ( ',    Coieockate ;    J>,   CEdogoniui 


constituting  surface  tension  play  a  part,  but  the  form  is  deter 
mined  chiefly  by  internal   forces   inherent   in  the  protoplasm. 

This  is  particularly  well   shown  when   such    organisms  extend 
delicate  protoplasmic   threads,  the   cilia,  and   maintain  these 

i47 


148 


PLANT    LIFE. 


in  active  motion  (fig.  168),  or  when  they  extend  a  portion  of 
the  body  as  a  pseudopodium  (fig.  169). 


FlG.   169. — Plasmodia,  creeping    bits   of   naked    protoplasm,   showing   varied   shapes 
parts  are  protruded  or  withdrawn.     Highly  magnified.-    Artel  Reiner. 


188.  Turgor. — If  the  organism  be  one  surrounded  by  a 
cell-wall,  or  if  it  be  made  up  of  a  number  of  cells  united,  the 
cell-wall  itself  plays  a  considerable  part  in  maintaining  the 
form.  This  is  due  to  the  condition  of  the  cell  known  as 
turgor.  When  fully  mature  the  cell-wall  of  each  active 
cell  is  lined  by  a  more  or  less  thick  layer  of  living  proto- 
plasm. In  the  interior  of  the  protoplasm  there  exist  one  or 
more  water  chambers,  the  vacuoles  (^[  5).  If  such  a  cell  as 
this  be  measured  in  its  normal  condition,  and  then  surrounded 
for  a  few  moments  l>v  a  10  per  cent,  solution  of  common  salt, 
reexamination  will  show  that  the  vacuoles  have  been  dimin- 
ished, the  protoplasm  shrunken  away  from  the  wall,  and 
remeasurement  will  show  that  the  cell  has  diminished  both  in 
length  and  diameter.  In  its  normal  condition,  therefore,  the 
wall  was  stretched  by  the  pressure  of  the  contents  within.  If 
a  cell  which  has  been  thus  shrunken  by  immersion  in  a  solu- 
tion of  salt  be  again  placed  in  water,  it  may  regain,  in  the 
course  of  a  few  hours,  its  original  condition,  that  is,  it  may 
again  become  turgid.  This  would  be  brought  about  by  the 
entrance  of  water  into  the  vacuoles  to  replace  that  withdrawn 
when  the  cell  was  placed  in  the  solution  of  salt. 

If  a  thin  piece  of  rubber  tubing  be  connected  with  a  pump 
and    filled    with    water   until    it    is   stretched,    it    increases    its 


THE   MAINTENANCE    OF  BODILY   FORM.        M9 

diameter  and  length  slightly,  and  gains,  at  the  same  time,  a 
condition  of  rigidity  greater  than  in  its  unstretched  condi- 
tion. In  a  similar  way  turgid  cells  are  more  rigid  than  those 
which  are  flaccid.  The  union  of  turgid  cells  produces  a 
member  more  rigid  than  one  in  which  the  cells  are  not  turgid. 
An  illustration  of  this  is  to  be  seen  in  the  condition  of  a 
wilted,  as  compared  with  a  fresh,  leaf.  The  turgor  of  thin- 
walled  cells  may  play  an  important  part  in  maintaining  the 
form  and  position  of  the  parts  of  a  plant. 

189.  Tissue  tensions. — But  turgor  can  affect  only  those  cells 
whose  walls  are  thin  and  extensible.  Those  whose  walls  have 
become  thick  and  rigid  are  not  stretched  by  this  force.  In 
the  larger  plants,  however,  where  both  thick-walled  and  thin- 
walled  tissues  exist,  it  is  possible  that  a  mass  of  thin-walled 
cells  may,  by  the  united  tension  of  its  component  cells, 
stretch  those  tissues  which  are  not  themselves  turgid.  Such 
strains  in  the  younger  regions,  particularly,  play  an  important 
role  in  maintaining  the  form  of  these  parts.  But  the  tensions 
in  the  older  parts  are  generally  due  to  the  unequal  growth  of 
different  tissues.    (See  ^|  259.) 

190.  Mechanical  rigidity. —  The  rigidity  of  the  cell-wall 
itself  must  be  relied  upon  by  all  the  larger  plants.  Certain 
tissues  are  specialized  by  having  their  cell-walls  greatly 
thickened,  and  such  tissue  regions  constitute  a  sort  of  frame- 
work or  skeleton,  which  is  filled  out  by  the  more  delicate 
tissues.  These  mechanical  tissues  are  so  distributed  within 
the  body  as  to  afford  frequently  the  maximum  resistance  to 
bending  and  breaking  strains.  In  the  accompanying  dia- 
grams the  position  of  the  mechanical  tissues  is  indicated  in 
transverse  sections  of  a  number  of  different  stems  (fig.  170). 
It  will  be  seen  that  they  illustrate  well-known  mechanical 
principles  in  their  distribution.  The  hollow  column  (E)  and 
the  [-beam  (A,  />',  C),  two  of  the  most  rigid  mechanical  con- 
structions, are  frequently  imitated  in  plants. 


ISO 


PLANT  LIFE. 


In  stems  of  trees  rigidity  is  secured  not  by  the  distribution 
of  the  mechanical  tissues,  but  by  their  massiveness.  In  them 
the  chief  mechanical  tissues  belong  to  the  wood,  which  forms 


Fig.  170.— Diagrams  showing  the  arrangement  of  mechanical  tissues  and  vascular 
bundles  in  the  cross-section  of  various  stems.  The  mechanical  tissue  is  gray;  the 
vascular  bundles  black,  with  white  dots.  A,  linden  (young) ;  B,  a  mint ;  C,  a  sedge  ; 
If,  a  bamboo  ;   A,  a  grass. — After  Kerner. 


a  solid  column  occupying  the  center  of  the  body.  Those 
plants  which  are  supported  by  the  medium  in  which  they 
live,  such  as  the  aquatic  plants,  are  usually  without  mechan- 
ical tissues. 


CHAPTER    XIII. 

NUTRITION. 

191.  Repair  and  growth. — Since  the  body  of  every  plant 
is  constantly  wasting  away  by  reason  of  its  own  activity,  it  is 
necessary  that  it  should  be  as  constantly  repaired.  It  must 
also,  for  a  considerable  time  or  throughout  its  whole  life,  be 
furnished  with  material  which  can  be  used  in  the  making  of 
new  parts.  Without  an  adequate  supply  of  food,  therefore, 
neither  repair  nor  growth  is  possible.  To  understand  what 
materials  are  necessary  for  repairing  waste  and  forming  new 
parts  of  the  living  plant,  the  constituents  of  a  plant  may  be 
determined  by  chemical  analysis. 

192.  Chemical  composition. — The  greater  portion  of  the 
weight  of  every  plant  is  found  to  be  water.  Of  the  firmer 
parts  it  forms  as  much  as  50  per  cent.,  while  of  the  softer 
parts  it  may  form  75  or  even  90  per  cent.  The  most  watery 
portions  of  some  plant  bodies,  such  as  the  juicy  portions  of 
fruits  and  the  whole  body  of  the  algae,  may  contain  only  2  to 
5  per  cent,  of  solid  matter.  The  solid  material,  left  after 
driving  off  the  water  at  a  temperature  of  no  ('.,  is  found  to 
consist  chiefly  of  three  elements,  carbon,  hydrogen,  and 
Oxygen.  The  most  abundant  element  in  addition  to  these  is 
nitrogen.  If  the  dry  substance  be  burned  these  four  elements 
are  driven  off  in  gaseous  forms,  and  there  remains  a  white 
material  which  crumbles  under  pressure,  the  ash.  An  analy- 
sis of  the  ash  reveals  the  presence  of  sulfur  and  phosphorus 
in  considerable  amounts,  and  also  smaller  quantities  of  the 
following   elements:    calcium,    magnesium,    potassium,    iron, 

151 


152  PLANT   T.TFE. 

sodium,  chlorine,  and  silicon.  Of  these  seven,  the  first  four 
are  found  in  the  ash  of  all  plants,  and  the  remaining  three 
are  very  common.  In  addition  to  the  elements  enumerated, 
about  25  others  are  known  to  occur  in  the  ash  of  plants,  but 
only  in  minute  quantities. 

A.  The  water  in  the  plant. 

193.  Necessity. — Since  water  forms  such  a  large  percent- 
age of  the  weight  of  fresh  plants,  it  is  manifest  that  it  must  be 
supplied  in  relatively  large  quantities,  if  the  plant  is  to  con- 
tinue in  an  active  condition.  A  portion  of  this  water  may 
be  used  up  in  the  chemical  changes  occurring  in  the  body, 
but  it  is  not  possible  to  discriminate  between  this  and  the 
water  which  is  necessary  to  furnish  the  proper  physical  con- 
ditions of  life.  Water  is  the  great  solvent  by  which  materials 
of  various  kinds  are  carried  into  the  plant  body,  and  1>\ 
which  a  still  greater  variety  within  it  are  transported  from 
plaGe  to  place.  Before  discussing  the  food  of  plants,  there- 
fore, the  relation  of  water  to  the  plant  may  be  examined. 

194.  Air,  water,  and  land  plants. — Some  plants  are  not  in 
contact  with  water  except  at  irregular  intervals.  These  are 
called  air  plants,  and  include  some  algae,  liverworts,  mosses, 
fernworts,  and  seed  plants.  All  these,  however,  are  able  to 
live  onlv  in  an  atmosphere  containing  large  quantities  of 
water  vapor,  or  in  those  regions  where  they  are  frequently 
sprayed  with  water.  Water  plants  float  upon  the  water,  or 
arc  submerged  in  it.  As  distinguished  from  both  air  and 
water  plants,  are  those  which  normally  have  the  mot  system 
and  sometimes  a  portion  of  the  stem  buried  in  the  soil,  con- 
tinually or  intermittently  in  contact  with  liquid  water,  while 
the  shoot  system  is  occasionally  sprayed  by  rain.  Such  may 
be  called  land  plants. 

195.  Solutions  in  water. — In  no  case,  however,  is  the 
water  in   which   plants  are    immersed,   or    with   which    they 


NUTRITION.  153 

are  sprayed,  pure  water.  It  always  holds  in  solution  sub- 
stances derived  from  the  atmosphere  or  from  the  soil  with 
which  it  has  come  in  contact.  These  substances  are  either 
organic  or  inorganic,  and  they  enter  the  plant,  along  with 
the  water,  through  those  organs  which  are  adapted  to  ab- 
sorption. 

196.  Absorption  of  water. — In  air  plants  of  the  simpler 
sorts,  any  parts  exposed  to  the  moist  air  or  rain  can  absorb 
water.  In  liverworts  and  mosses  the  thallus  or  the  leaves 
are  active  absorbents.  In  the  higher  plants,  such  as  the 
aerial  orchids,  the  external  cortex  of  the  roots  is  especially 
adapted  to  absorb  liquid  water,  or  to  condense  the  water 
vapor  of  the  atmosphere.*  In  water  plants  the  surfaces  which 
are  normally  in  contact  with  the  water  are  absorbing  surfaces. 
Such  plants  may  be  either  wholly  without  a  root  system,  or  it 
may  be  only  sufficiently  developed  to  anchor  them  in  the 
mud.  In  land  plants  the  root  system  is  especially  adapted  to 
the  absorption  of  water.  Only  minute  quantities  of  water 
are  absorbed  by  the  leaves  and  other  aerial  parts.  The  re- 
vival of  a  wilted  plant  by  spraying  seems  to  be  due  more 
largely  to  checking  the  loss  of  water  by  evaporation  than  to 
the  slight  absorption  which  may  occur.  The  root  system  of 
the  land  plants  is  developed  in  contact  with  the  soil. 

197.  Soil. — The  soil  consists  primarily  of  finely  divided 
particles  of  rock,  whose  nature  and  size  determine  the  quali- 
ties by  which  soils  are  ordinarily  distinguished  into  gravelly, 
sandy,  loamy,  clayey,  etc.  Mixed  with  these  rock  panicles 
is  more  or  less  organic  material  derived  from  the  offal  of 
plants  or  animals.  When  decaying  plant  offal  predominates, 
the  soil  is  known  as  vegetable  mold  or  humus,  which  natu- 
rally forms  the  upper  layer  of  the  soil  of  forests.  To  garden 
or   field  soils,  not   naturally  rich   in   organic   matter,  this    is 

*  If  such  condensation  really  occurs  (as  is  generally  alleged),  it  does 
not  suffice  to  keep  the  plants  supplied  with  the  required  amount  of  water. 


54 


rLANT   LIFE. 


frequently  added  artificially.  Both  manure's  and  artificial 
fertilizers  (the  latter  consisting  usually  of  dried  and  ground 
animal  offal)  arc  added  chiefly  for  the  purpose  of  supplying 
compounds  of  nitrogen  and  phosphorus. 

198.  Soil  water. — No  matter  how  fine  the  soil  may  be,  the 
rock  particles  are  not  in  close  contact,  but,  on  account  of 
their  angular  outline,  leave  spaces  of  greater  or  less  size  to  be 
occupied  by  other  materials.  If  a  soil  be  examined  immedi- 
ately after  a  heavy  rain-fall,  these  spaces  will  be  found  com- 
pletely occupied  by  rain-water.      If  the  soil  be  so  situated  as 


Fig.  171.— Diagram  of  a  portion  of  soil  penetrated  by  root  hairs,  h.  A',  arising  from 
root,  ''.  At  =,  .f,  ,v'  (lie  hair  lias  grown  into  contact  with  sonic  of  the  soil  particles,  /. 
which  are  surrounded  by  water  films  (shaded  by  parallel  lines),  0,  o,  t.  The  white 
spaces  are  air  bubbles,  S,  &',  y,  y' .  When  water  enters  the  hair  .it  a,  the  thickness  of 
the  film  a,  3,  t  will  be  diminished,  and  some  water  will  flow  towards  this  point,  re- 
ducing all  the  other  water  films  in  the  vicinity.  Move  air  enters  from  above.  When 
rain  falls,  the  reverse  process  occurs;  the  films  thicken,  and  the  air  may  be  entirely 
driven  out,  to  return  as  the  surplus  water  drains  away.      After  S.u  lis. 

to  be  naturally  drained,  considerable  quantities  of  this  water 
will  disappear  gradually,  and  the  larger  spaces  between  the 
soil  particles  will  be  occupied  partly  by  films  of  water  adherent 
to  the  soil  grains,  and  partly  by  bubbles  of  air  (fig.   171). 

199.  Salts  dissolved. — The  water  which  thus  filters 
through  the  soil  dissolves  and  retains  certain  of  its  constitu- 
ents.     As  the  rain  passes  through   the  atmosphere  it  also  dis- 


NUTRITIOX.  155 

solves  certain  substances  found  therein,  notably  minute  quan- 
tities of  ammonia  and  nitrous  acid.  By  this  means  compounds 
containing  nitrogen  are  constantly  being  brought  to  the  soil 
by  the  rain. 

200.  Root  absorption. — The  structure  of  the  root  system 
has  been  explained  (%  78-82).  The  root  hairs  come  into 
close  contact  with  the  soil  particles,  pushing  them  aside 
somewhat,  and  being  in  turn  more  or  less  deformed  by  their 
resistance  (z,  s,  fig.  171).  So  close  does  the  contact  of  the 
root  hairs  and  soil  grains  become  that  many  particles  of  the 
soil  are  imbedded  in  the  walls  of  the  root  hairs  (fig.  84). 
The  root  hairs  are  not  only  in  contact  with  the  soil  particles, 
but  also  with  the  films  of  water,  which  occupy  the  spaces  be- 
tween them  (a,  fig.  171).  They  are  thus  in  a  position  for 
absorbing  water  from  the  adjacent  films. 

201.  Limit  of  absorption. — Not  only  is  the  water  im- 
mediately in  contact  with  the  root  a  source  of  supply,  but 
even  that  in  the  deeper  and  more  distant  parts  of  the  soil. 
For  when,  by  the  entrance  of  some  water  into  the  root  hair, 
the  thickness  of  that  layer  has  been  decreased,  the  disturbance 
of  equilibrium  causes  a  flow  from  neighboring  layers  to 
equalize  again  the  surface  tensions.  This  goes  on  until  the 
films  of  water  upon  the  soil  grains  become  so  thin  that  the 
water  particles  are  held  too  tenaciously  to  be  pulled  away  by 
the  root.  There  remains  in  such  exhausted  soil,  which  seems 
dry  as  dust  to  the  touch,  2  to  1 2  per  cent  of  water  unavailable 
for  the  plant. 

202.  Solvent  action. — The  root  hairs  also  exert  a  slightly 
solvent  action  upon  the  soil  particles  themselves  by  reason  of 
the  carbonic  acid  and  the  acid  salts  which  they  excrete.  By 
this  means  various  minerals,  especially  carbonates  of  lime  and 
magnesia  (limestone),  which  could  not  be  dissolved  by  the 
water  alone,  may  be  brought  into  solution. 

Water  enters  the  root  hairs  by  the  physical  process  known 


156  PLANT  LIFE. 

as  osmosis,  the  protoplasm,  braced  by  the  cell-wall,  acting  as 
the  membrane,  and  the  cell  sap  of  the  vacuole  as  the  denser 
fluid  of  the  osmotic  pair.      (See  Physics.) 

203.  The  development  of  the  root  system  is  related  to 
the  character  of  the  soil  and  to  the  amount  and  distribution 
of  water  and  organic  matter  within  it.  Branching  of  the 
root  system  is  much  more  profuse  in  the  moister  parts  of  the 
soil,  as  well  as  in  those  which  contain  more  organic  matter. 

204.  Movement  of  water  within  the  plant. — Once  the 
water  has  gained  entrance  to  the  plant,  it  must  move  to  those 
parts  where  it  is  to  be  used — i.e.,  to  all  the  organs  of  the 
plant,  but  especially  to  the  leaves,  since  from  these  there  is 
the  largest  loss  of  water  by  evaporation  (^[  209).  From  the 
root  hairs  the  water  passes  inward  through  the  cells  of  the 
cortex,  and  reaches  the  stele.  The  forces  which  determine 
this  movement  and  its  direction  are  not  fully  understood, 
though  osmosis  probably  plays  a  chief  part.  They  are  com- 
prehended under  the  general  phrase  root  pressure. 

205.  Root  pressure. — The  action  of  root  pressure  may  be 
demonstrated  by  severing  a  suitable  stem  close  to  the  ground 
and  observing  the  water  which  flows  out,  after  a  short  time, 
from  the  cut  end.  Careful  examination  of  the  cut  surface 
will  show  that  the  water  oozes  out  chiefly  from  the  woody 
parts  of  the  stele.  The  force  with  which  water  is  extruded 
may  be  measured  by  attaching  to  the  stump,  by  means  of  a 
rubber  tube,  a  manometer  (fig.  172).  In  this  way  it  may  be 
ascertained  that  in  woody  plants,  such  as  the  birch,  the 
pressure  sometimes  becomes  equal  to  that  of  five  or  six 
atmospheres. 

206.  Route  to  the  leaves. — After  entering  the  xylem 
bundles  of  the  roots,  the  water  is  thence  transferred  along  the 
stem  in  the  same  tissues,  which  are  continuous  with  those  of 
the  root.  Since  the  xylem  bundles  form  an  unbroken  line  to 
the  most  remote  parts  of  the  leaves,  passing  out  in  the  ribs 


NUTRITION. 


157 


and  forming  the  finer  veins,  the  water  may  be  distributed  to 

every  part  of  the  plant  body.     Within 

the  wood  it  travels  chiefly  in  the  cavities 

of  the  large  ducts  or  vessels,  when  these 

are  present,  though  the  walls,  also,  are 

saturated  with   it,   and  permit  a  slower 

movement.      These    ducts,   although    of 

great  relative  length  (some  up  to  1  m.), 

are  not  continuous  tubes  like  the  veins 

of  an  animal,  nor  are  they  filled   with 

water.      The  water  is  broken   into  short 

columns  by  numerous  gas-bubbles,    and 

in  ascending  to  any  considerable  height 

must  traverse  many  cell-walls. 

207.  Motive  power. — The  force  by 
which  water  is  raised  in  the  larger  plants 
remains  yet  to  be  ascertained.  The 
water  does  not  flow  along  the  ducts  in  a 
continuous  current,  as  the  blood  in  the  Flm 
veins,  propelled  by  a  force  behind,  for 
root  pressure  is  not  adequate  to  push  it  to 
the  height  attained.  On  the  contrary, 
during  the  times  of  most  active  evapo- 
ration from  the  leaves,  i.e.,  when  the 
greatest  supply  is  needed,  root  pres- 
sure becomes  almost  or  quite  negative. 
Capillarity  is  also  inadequate.  The 
diameter  of  the  largest  ducts  is  too  small 
and  the  friction  of  the  water  against 
their  sides  consequently  too  great  to 
permit  the  movement,  by  this  means,  of  ln,/ 
a  sufficient  amount  of  water  to  supply  the  evaporation. 
Moreover,  the  interruption  of  the  water  columns  by  gas- 
bubbles  produces  surface  tensions  which  quite  overcome  that 


a  T-tube,  R,  is  attached  by 
a  piece  of  rubber  tubing, 
v.  The  other  openings  are 
closed  by  rubber  corks,  k, 
through  one  of  which 
jussr--  ,1  small  glass  tube, 
r,  bent  into  two  unequal 
legs,  containing  mercury. 
Through  the  upper  should 
pass  a  short  piece  oi  glass 
tubing  drawn  out  to  a  line 
point,  to  be  sealed  off  in  a 
flame  after  A'  is  filled  with 
water.  At  the  beginning  of 
the  experiment  the  mercury 
is  about  at  the  same  level 

in  both  legs.  As  water  is 
ton  ed  from  tin-  stump  into 
A'  by  toot  pressure  the  mer- 
lin v  rives  in  the  .inn  f' 
and  falls  correspondingly 
Alter  SachS, 


158  PLANT   LIFE. 

of  capillarity.  It  has  been  found  that  the  bubbles  of  gas 
here  mentioned  often  exist  under  negative  pressure,  as  shown 
by  the  fact  that  a  stem  cut  under  mercury  allows  the  mercury 
to  ascend  for  some  distance  within  the  vessels.  This  negative 
pressure  of  the  gases  is  due  to  the  evaporation  of  water  from 
the  leaves,  and  the  most  recent  researches  point  to  this  as  a 
very  important  or  even  the  chief  factor  in  lifting  the  water. 
That  the  movement  is  not  a  function  of  living  cells  is  shown 
by  experiments  in  which  stems  of  plants  have  been  subjected 
to  poisonous  agents,  or  heated  for  many  hours  to  a  degree 
sufficient  to  kill  all  the  living  cells,  yet  without  materially 
affecting  the  supply  of  water. 

208.  The  loss  of  water. — Water  is  constantly  evaporating 
from  the  whole  surface  of  the  plant  exposed  to  the  air.  Since 
this  loss  is  probably  more  or  less  modified  by  the  vital  activ- 
ity of  the  plant,  it  has  received  the  special  name,  transpira- 
tion. 

f—  I     209.   Transpiration. — In  the  higher  plants    transpiration 
from  the  surface  is  reduced  by  the  waterproofing  of  the  epi- 
dermis, so  that  most  of  it  takes  place   from   the  surfaces  of 
internal   cells    into   the   intercellular   spaces,    wherever   these 
exist.      Since  the  intercellular  spaces  are  connected  with  each 
other   and  also,    through  the  stomata.   with   the  outside  air, 
water  vapor  is  constantly  passing  off  by  diffusion.    The  leaves, 
affording  the  largest  exposure,  are  especially  organs  of  trans- 
piration.     After  they  have  become  fully  expanded  no  appre- 
ciable amount  of  water  is  lost  directly  from  their  surfaces. 
I       210.   Amount  and  regulation. — The  amount  of  transpira- 
/    tion,  therefore,  varies  with  the  structure  of  the  leaf  rather 
/    J    than  with  its  area.     The  temperature,  percentage  of  water 
*  and  movements  of  the  air  affect  profoundly  the  rapidity  of 
transpiration.      Hence  arises  the  need  of  regulation  by  the 
plant,    to   prevent  excessive   loss.      The  guard  cells   of  the 
stomata  are  irritable,  so  that  external  conditions  affect  their 


NUTRITION.  1 59 

turgor,  [f  both  arc  turgid,  they  become  curved  away  from 
each  other  so  as  to  increase  the  size  of  the  opening  between 
them.  If  they  are  flaccid,  the  thick  ridges  along  the  inner 
face  of  each  cell  straighten  them,  and  so  close  the  orifice 
more  or  less  completely  (figs.  161,  162).  The  presence  or' 
absence  of  hairs  upon  the  leaves,  the  existence  of  stomala 
upon  one  or  both  surfaces,  the  sinking  of  the  guard  cells 
below  the  general  leaf  surface,  the  distribution  of  the  stomat; 
the  thickening  of  the  leaves,  their  inrolling  (fig.  357),  or 
revolution  (fig.  359),  have  a  decided  effect  upon  the  rate  of 
transpiration,  and  may  be  adapted  to  regulate  it.  (See 
1T434ff.) 

B.     Foods  in  general. 

211.  Foods. — In  addition  to  an  adequate  supply  of  water, 
food  is  required.  Materials  consumed  by  plants  as  food  are 
either  organic  or  inorganic.  Organic  materials  are  those 
which  have  been  produced  in  nature  by  the  chemical  changes 
occurring  within  living  bodies.  Inorganic  materials  are  those 
formed  in  nature  by  chemical  reactions  not  occurring  in  con- 
nection with  a  living  body.  A  very  few  of  the  simplest  plants 
(bacteria)  have  been  grown  by  the  use  of  inorganic  materials 
alone;  only  the  minutest  quantities  of  such  substances  are 
utilized  by  most  plants  as  food  ;  but  large  amounts  are  used 
by  all  green  plants  for  the  manufacture  of  organic  foods. 

Organic  foods  are  of  three  kinds,  carbohydrates,  fats,  and 
proteids. 

212.  Carbohydrates  are  substances  consisting  of  carbon, 
hydrogen  and  oxygen,  so  proportioned  that  there  are  6 
carbon  molecules  (or  some  multiple  of  6)  while  the  two  latter 
elements  are  combined  in  the  ratio  of  two  parts  of  hydrogen 
to  one  of  oxygen.  Well-known  examples  are  sugars  and 
starch. 


l6o  PLANT   LIFE. 

213.  Fats. — These  arc  likewise  combinations  of  the  same 
three  elements,  but  in  them  the  hydrogen  and  oxygen  do  not 
exist  in  the  ratio  of  two  to  one,  the  oxygen  being  much  less 
in  proportion.  Some  are  solid  at  ordinary  temperatures, 
while  others  are  fluid.  They  are  combinations  of  free  fatty 
acids  and  glycerin.  Upon  the  addition  of  an  alkali,  the  fatty 
acids  combine  with  it  to  form  soap  and  other  compounds  ot 
less  amount  while  the  glycerin  is  set  free  Commercial  ex- 
amples of  plant  fats  are  olive  oil,  linseed  oil,  and  cacao  butter. 

214.  Proteids  are  foods  consisting  of  at  least  five  and 
generally  of  six  elements,  namely,  carbon,  hydrogen,  oxygen, 
nitrogen,  sulfur,  and  (ordinarily)  phosphorus.  These  elements 
are  complexly  combined  in  varying  proportions.  Proteids 
are  generally  recognizable  by  their  property  of  coagulation 
upon  the  application  of  heat,  acids,  or  other  agents.  Well- 
known  examples  are  the  proteids  forming  the  "white  of  egg." 
Examples  from  the  vegetable  kingdom  are  less  familiar. 

Proteids  always,  and  either  carbohydrates  or  fats,  or  both, 
must  be  available  in  order  that  a  plant  may  be  properly 
nourished.  Green  plants  obtain  their  food  chiefly  by  manu- 
facturing it  out  of  inorganic  materials  taken  into  the  plant 
body  from  without.  They  are  the  only  organisms,  so  far  as 
known,  which  have  the  power  of  building  up  organic  material 
from  inorganic.  They  are,  therefore,  the  ultimate  source  of 
the  food  supply  of  the  world. 

215.  Metabolism. — After  suitable  foods  become  available 
to  plants,  whether  by  manufacture  or  by  absorption  ready- 
made,  they  suffer  various  chemical  changes  both  before  and 
after  becoming  a  part  of  the  body.  The  changes  by  which 
foods  are  manufactured  and  assimilated  and  those  by  which 
the  products  of  waste  are  gotten  rid  of  are  all  comprehended 
under  the  term  metabolism. 


NUTRITION.  l6l 

C.    Nutrition   of  colorless  plants. 

216.  Colorless  plants. — By  tin's  really  inaccurate  phrase 
are  meant  plants  which  do  not  possess  chlorophyll,  though 
some  of  them  are  highly  colored  by  other  pigments. 

The  colorless  plants  among  the  thallophytes  constitute  two 
large  groups,  known  as  bacteria  and  fungi.  Among  the  seed 
plants,  also,  are  found  some  devoid  of  chlorophyll. 

Many  plants  possessing  chlorophyll  show  to  the  eye  other 
tints  than  green,  when  other  pigments  are  present  in  such 
quantity  as  to  mask  the  green.  This  is  notably  the  case  with 
the  so-called  "foliage  plants,"  in  which  reds,  yellows,  pur- 
ples, and  browns  are  common.    (See  also  ^|*[  n,  40,  45.) 

Colorless  plants  necessarily  live  either  upon  the  decomposi- 
tion products  of  dead  organisms,  or  in  company  with  living 
organisms.  Those  which  live  upon  dead  bodies,  whether 
these  have  lost  their  form  completely  or  not,  are  known  as 
saprophytes.  Those  organisms  which  live  in  association  one 
with  another  are  called  symbionts  and  their  relation  is  known 
as  symbiosis.  (See  Chap.  XXIV.)  Some  symbionts  are 
antagonistic  and  stand  in  the  relation  of  parasite  and  host, 
the  name  parasite  being  applied  to  the  organism  which 
depends  for  its  food  upon  the  supporting  organism,  called  the 
host. 

217.  Saprophytes  and  parasites  may  be  either  obligate  or 
facultative.  <  )bligate  parasites  or  saprophytes  are  those  which 
can  exist  only  upon  living  or  upon  dead  organisms,  respec- 
tively. Facultative  parasites  or  saprophytes  are  those  which 
can  pass  a  portion  of  their  existence  upon  decaying  or  upon 
living  organisms,  respectively.  They  are  not  able,  however, 
to  complete  their  life  cycle  except  upon  their  appropriate 
substratum. 

218.  Saprophytes. — Saprophytic  bacteria  live  immersed 
in   solutions   of  organic    material,  or  surrounded   by  films  of 


1 62  PLANT  LIFE. 

fluid  on  the  surface  or  in  the  interior  of  the  organic  material 
upon  which  they  flourish.  Saprophytic  fungi  either  form 
their  mycelium  upon  the  surface  of  the  organic  matter,  or, 
more  commonly,  they  penetrate  it  more  or  less  extensively 
by  a  profusely  branched  system  of  submerged  hyphae.  A  few 
saprophytic  seed  plants  form  at  the  base  of  the  stem  an  en- 
larged, tuber  dike  mass  from  whose  surface  great  numbers  of 
profusely  branched  roots  arise.  These  penetrate  the  decay- 
ing material  in  all  directions,  and  act  as  absorbing  organs. 
A  few  have  abundantly  branched  underground  stems  and 
have  no  permanent  roots. 

219.  Digestion. — Saprophytes  whose  surfaces  are  sur- 
rounded by  food  solutions  have  only  to  absorb  them.  Some, 
however,  have  power  to  convert  into  material  soluble  in  water 
the  solid  insoluble  foods  with  which  they  are  in  contact. 
This  is  brought  about  either  by  a  direct  action  of  the  proto- 
plasm of  the  living  plant,  or  by  means  of  enzymes  (•([  237) 
excreted  by  it.  Such  chemical  changes,  by  means  of  which 
insoluble  solid  materials  are  transformed  into  soluble  ones 
and  are  dissolved,  are  quite  like  those  which  occur  in  the  di- 
gestive tract  of  the  higher  animals,  and,  therefore,  may  Im- 
properly termed  digestion. 

220.  Assimilation. — After  the  food  is  absorbed,  it  under- 
goes various  changes,  collectively  known  as  assimilation,  by 
which  it  is  enabled  to  become  part  of  the  living  material  of 
the  plant  body.* 

221.  Fermentation  and  putrefaction. — Some  saprophytes 
produce  changes  in  the  material  upon  or  in  which  they  grow, 
other  than  those  described  above.  The  more  important 
changes  may  be  comprehended  under  the  two  terms  fermen- 
tation  and   putrefaction.      Between  these  there   is  no  sharp 

*  This  is  not  to  be  confused  with  the  manufacture  of  organic  food  by 
green  plants,  to  which  the  term  assimilation  is  inaptly  applied  by  most 
writers. 


NUTRITION.  163 

line  of  demarcation.  Popularly  the  term  putrefaction  is  ap- 
plied to  the  changes  in  nitrogenous  substances  which  are  ac- 
companied by  offensive  odors.  Fermentation  is  commonly 
applied  to  the  chemical  changes  occurring  in  sugary  solutions, 
such  as  fruits,  expressed  juices,  infusions,  etc.  Many  bacteria 
and  a  number  of  fungi,  notably  those  known  as  yeasts,  are 
capable  of  producing  fermentation  in  such  solutions.  The 
chemical  changes  produced  are  more  extensive  than  those 
required  for  obtaining  food.  Ordinary  brewer's  yeast,  for 
example,  utilizes  about  5  per  cent  of  the  sugar  present  in  the 
solution  for  food,  but  breaks  up  the  remaining  95  per  cent 
into  carbon  dioxide,  alcohol,  and  some  other  less  important 
by-products.  In  putrefaction  the  by-products  are  commonly 
offensive  gases,  among  which  hydrogen  sulfid  (H„S)  predomi- 
nates. A'arious  other  materials  may  be  formed,  among  which 
not  infrequently  are  virulent  poisons.  These  are  well  known 
in  certain  putrefactive  changes  of  milk,  meat,  etc. 

222.  Parasites  obtain  their  food  either  by  growing  upon 
the  surface  of  the  host  and  thrusting  into  its  interior  absorb- 
ing organs  ;  or  by  growing  wholly  in  the  interior  of  the  host, 
breaking  out  to  its  surface  only  to  form  reproductive  bodies. 

Parasites  may  work  little  apparent  harm,  or  they  may  bring 
about  local  disease  and  death  of  the  host.  Their  mode  of 
obtaining  food  is  not  essentially  different  from  that  of  sapro- 
phytes. They  either  digest  solid  foods,  or  absorb  liquid 
foods,  prepared  by  the  host  for  its  own  use.  Among  the 
green  plants  there  are  some  partial  parasites,  sin  h  as  the  mis- 
tletoe, which  seem  to  obtain  from  their  hosts  chiefly  the 
water  and  salts  which  they  have  absorbed.  These  materials 
they  themselves  elaborate  into  food.      (See  further  «j  465.) 

D.  Nutrition  of  green  plants. 

223.  Raw  materials. — In  order  that  the  green  plants  may 
be  able  to   manufacture   their   food,  they  require  certain   raw 


164  PLANT   LIFE. 

materials,  which  arc  obtained  from  the  medium  by  which 
they  are  surrounded.  These  substances  are  a  weak  watery 
solution  of  various  mineral  salts,  and  a  gas,  carbon  dioxide. 

224.  Salts  absorbed. — Along  with  the  water  which  is 
taken  into  the  plant  go  various  amounts  of  dissolved  material, 
a  considerable  portion  of  which  consists  of  mineral  salts. 
When  plants  grow  in  humus,  or  in  water  or  soils  containing 
organic  matter,  a  variable  amount  of  carbon  compounds 
suited  for  food  may  be  dissolved  by  the  water  and  be  taken 
up  by  the  plant.  To  this  extent  the  plant  will  live  as  a  sapro- 
phyte, and  no  doubt  many  field  and  garden  plants  have  been 
bred  to  require  this  sort  of  life.  Among  the  mineral  salts 
the  most  important  are  the  salts  of  calcium  and  magnesium, 
which  are  present  in  all  soils,  in  greater  or  less  quantity, 
usually  in  the  form  of  nitrates,  phosphates,  and  sulfates. 
Compounds  of  two  other  indispensable  elements,  namely, 
iron  and  potassium,  are  dissolved  in  soil  waters.  In  the 
same  way  at  least  seven  additional  elements  are  obtained  by 
plants.  Besides  these,  other  compounds  to  a  considerable 
number,  of  no  use  in  forming  food,  are  taken  in.  Silicon, 
for  example,  which  is  found  in  the  ash  of  almost  all  plants,  is 
of  no  value  either  as  a  food,  or  for  the  manufacture  of  food, 
although  it  plays  an  important  role  in  increasing  the  rigidity 
of  certain  plants,  and  in  protecting  others  from  injury. 

225.  Selective  action. — Compounds  of  these  elements 
exist  in  the  water  in  various,  though  small,  amounts.  But 
they  are  not  taken  into  the  plant  in  the  same  proportions  as 
they  exist  in  the  water.  For  each  substance  presented  to  the 
plant  there  is  a  certain  degree  of  concentration  at  which  its 
solutions  are  absorbed  with  greater  rapidity  than  at  any  other. 
Substances  which  are  utilized  by  the  plant  and  which,  there- 
fore, disappear  as  such  within  it  by  having  their  chemical  com- 
position altered  or  by  being  stored  up  in  a  different  form 
and  so  removed    from  solution,  will  enter  the   plant  contin- 


NUTRITION.  165 

uously  so  long  as  the  supply  outside  exists.  Substances  ab- 
sorbed by  the  plant  and  not  utilized  accumulate,  and  their 
solutions  soon  attain  the  same  degree  of  saturation  within  the 
plant  as  outside,  when  they  cease  to  be  absorbed.  It  is  for 
this  reason  that  two  plants  growing  upon  the  same  soil  may 
contain  very  unequal  quantities  of  any  important  material. 
Plants  thus  exert  a  sort  of  selective  action,  but  this  selection 
is  dependent  upon  purely  physical  laws,  and  is  not  directly 
under  the  control  of  the  plant. 

226.  Carbon  dioxide. — Carbon  dioxide,  as  such,  is  not 
found  in  nature.  It  instantly  combines  with  water  to  form 
a  gas  known  as  carbonic  acid  gas,  and  this  is  ordinarily 
meant  when  carbon  dioxide  is  spoken  of.  This  gas  exists  in 
small  quantities  in  the  atmosphere,  rarely  exceeding  one  part 
in  twenty-five  hundred,  except  in  secluded  spaces.  The 
constant  currents  in  the  atmosphere  make  its  distribution 
practically  uniform.  On  account  of  its  ready  solubility,  this 
gas  also  exists  in  abundance  in  soil  waters  and  in  the  larger 
bodies  of  water  constituting  streams,  lakes,  or  pools.  In  a 
soil  containing  carbon  compounds  it  is  constantly  being  pro- 
duced by  decomposition.  The  water  which  passes  through 
the  soil  therefore  has  a  larger  percentage  of  this  gas  than  the 
air,  sometimes  containing  as  much  as  one  per  cent. 

227.  Absorption. — Water  plants  readily  absorb  the  dis- 
solved gas  by  such  surfaces  as  are  exposed  to  the  water. 
Floating  plants  have  opportunity  to  obtain  it  both  from  the 
water  and  from  the  atmosphere.  Land  plants,  although 
their  roots  are  surrounded  by  a  comparatively  concentrated 
solution  of  carbonic  acid,  do  not  take  up  appreciable  quan- 
tities by  these  organs.  On  the  contrary,  the  absorption  of 
this  gas  seems  to  depend  entirely  upon  those  cells  which 
contain  chlorophyll.  The  Stomata,  which  allow  the  internal 
intercellular  spaces  free  communication  with  the  outside  air, 
are   important  organs,  not   only  in    regulating   transpiration, 


1 66  PLANT  LIFE. 

but  also  in  permitting  the  absorption  of  this  gas.  Its  con- 
tinued absorption  depends  upon  its  continuous  removal  from 
the  cell  sap  in  the  manufacture  of  carbohydrates. 

228.  Anabolism. — By  this  term  arc  designated  the  con- 
structive processes  of  metabolism,  by  which  complex  sub- 
stances are  produced  from  simple  ones.  These  materials 
belong  chiefly  to  two  classes,  {a)  carbohydrates,  (b)  proteids. 

229.  i.  Carbohydrates. — The  process  by  which  carbo- 
hydrates are  produced  is  called  photosyntax.  The  conditions 
under  which  photosyntax  occurs  are  three  :  (a)  the  presence 
of  chlorophyll,  (b)  the  action  of  light,  and  (c)  the  presence 
of  potassium  salts. 

230.  (a)  Chlorophyll. — Chlorophyll,  as  has  been  shown 
in  Part  I,  sometimes  colors  the  whole  protoplasm  of  the  cell, 
but  is  more  commonly  found  only  in  certain  special  struc- 
tures, the  chlorophyll  bodies.  The  real  work  of  forming  the 
carbohydrate  depends,  therefore,  upon  the  protoplasm  of  the 
chlorophyll  body.  The  purpose  of  the  chlorophyll  is  to 
absorb  certain  portions  of  the  light  which  falls  upon  it.  If 
the  light  which  has  been  passed  through  a  green  leaf,  or  a 
solution  of  chlorophyll,  be  examined  with  a  spectroscope, 
seven  dark  bands  appear  in  place  of  certain  of  the  colored 
rays,  because  these  have  been  stopped  by  the  chlorophyll 
(fig.  173).  ( >ne  absorption  hand  lies  between  the  red  and  the 
orange  (  3-9  of  scale,  fig.  1  73),  another  in  the  orange  ( 1 1-14), 
the  third,  faint,  in  the  yellow  (17-20),  the  fourth  at  the 
edge  of  the  green  (30—32),  while  the  fifth  (53-73),  sixth 
(75-93),  and  seventh  (94-100)  bands  occupy  most  of  the 
blue  and  violet.  These  last  three  blend  into  one  extremely 
broad  band,  except  when  the  light  passes  through  very  small 
quantities  of  chlorophyll. 

231.  (6)  Light. — The  light  absorbed  by  the  chlorophyll 
furnishes  the  energy  necessary  to  carry  on  the  work  of  taking 
apart  the  carbonic  acid  and  rearranging  the  molecules  into  a 


NUTRITION. 


167 


more  complex  substance.  This  energy  cannot  be  supplied 
by  the  plant  itself.  An  external  source  of  energy  is  therefore 
necessary.      What  this  source  is  is  unimportant,  provided  the 


Fig.  173. — The  absorption  spectrum  of  an  alcoholic  solution  of  chlorophyll.  A  beam 
of  sunlight  passed  through  a  prism  is  broadened  into  a  strip,  called  the  spectrum, 
which  shows  different  colors,  according  to  the  length  of  the  light  waves,  the  longest 
appearing  red  and  the  shortest  violet.  Some  of  the  light  waves  are  stopped  by 
absorption,  and  at  these  places  black  lines  appear  (Fraunhofer  lines),  the  more  im- 
portant being  those  below  the  letters  B,  <-',  etc.     When  the  sunlight  passes  through  an 


alcoholic  solution  it  absorbs  those  parts  of  the  light  corresponding  to  the  dark  bands 

lade  visible  ' 

:he  Fran 
or  roughly  by  the  colors. — After  Kraus. 


I  to  VII.   These  absorption  bands  are  made  visible  by  spreading  out  the  light  ray  into 
a  spectrum.     The  bands  are  located  by  the  Fraunhofer  lines,  or  by  the  artificial  scale, 


energy  be  sufficiently  intense.  The  light  of  an  electric  arc 
serves  the  purpose  as  well  as  sunlight,  if  its  intensity  be 
equal. 

232.  (c)  Potassium  salts. —  These  take  no  part  in  the 
composition  of  the  food  produced,  and  their  exact  role  is  not 
understood.  It  is  well  established,  however,  that  their 
presence  is  essential  to  the  formation  of  the  carbohydrate. 

233.  The  product  of  photosyntax. — The  steps  in  the 
process  of  the  building  of  carbohydrates  are  not  thoroughly 
known.  Present  indications  are  that  the  material  first  pro- 
duced by  the  rearrangement  of  the  molecules  of  carbon, 
hydrogen,  and  oxygen,  derived  from  the  carl  ionic  acid,  is  a 
molecule  of  the  simplest  carbohydrate,  formaldehyde.  CI  !..<  >. 
Several  of  these  are  then  built  up  (by  condensation  and 
polymerization)  into  one  of  the  more  complex  carbohydrates, 
such  as  cane  sugar.  Starch  is  generally  the  first  visible  prod- 
uct and   appears  as   minute  granules  in   the   interior  of  the 


1 68  PLANT  LIFE. 

chlorophyll  bodies,  but  is  probably  a  transformation  product 
from  a  sugar,  to  whi'ch  it  is  closely  akin  (hemic  ally. 

234.  2.  Proteids. — The  formation  of  proteids  is  even 
more  obscure.  Apparently  at  some  point  in  the  series  of 
changes  following  the  formation  of  formaldehyde,  molecules 
of  nitrogen  are  added  to  form  an  amid.  Amids,  especially 
asparagin,  leucin,  and  tyrosin,  are  common  in  plants.  They 
may  also  be  produced  by  the  use  of  carbon,  hydrogen,  and 
oxygen  from  complex  carbohydrates  by  katabolism  (*  238). 
They  are  soluble  in  water,  crystallizable,  and,  hence,  can  be 
carried  by  osmosis  from  cell  to  cell.  From  these,  by  the 
addition  of  sulfur  and  phosphorus,  proteids  are  formed,  but 
neither  the  steps  in  the  process  nor  its  conditions  are  well 
understood.  Apparently  the  formation  of  amids  occurs  in 
green  tissues  and  under  the  influence  of  light.  It  is  probable 
that  even  among  the  green  plants  the  formation  of  proteids 
takes  place  in  other  parts  than  the  green  tissues,  as  it  is 
certain  that  this  occurs  also  among  the  colorless  plants.  The 
proteids  which  are  built  up  from  the  amids  are  used  directly 
in  the  repair  of  protoplasm.  Since  carbohydrates  are  neces- 
sary to  the  formation  of  proteids,  and  since  they  can  be 
manufactured  only  by  the  green  plants  under  the  influence  of 
light,  it  will  be  seen  how  essential  these  plants  are  for  the 
world's  food  supply. 

E.    Storage  and   translocation   of  food. 

235.  Storage  and  transfer,  -both  in  the  colorless  and 
green  plants  it  is  necessary  that  the  foods  made  or  absorbed 
should  be  transferred  from  one  point  to  another  where  they 
are  to  be  used.  The  larger  the  plant,  the  more  important 
does  this  transfer  become.  In  many  plants,  also,  it  is 
desirable  that  a  supply  of  reserve  food  be  stored  for  use  when 
a  supply  is  no  longer  available  from  the  outside  or  by 
manufacture. 


NUTRITION. 


1 69 


236.   Storage. — In   the   higher   plants  storage   places  are 
secured  by  the  enlargement  of  roots,  stems  or  leaves,  to  form 


Fig.  174.— Reserve  starch.  .-/.  two  cells  of  a  potato,  showing  enclosed  starch  grains 
The  other  contents  not  shown.  A',  compound  starcli  grains  from  a  grain  of  oats 
Three  of  the  component  granules  of  a  large  grain  are  shown  separately.  (',  starch 
giains  from  a  bean.     All  highly  magnified.— After  kerner. 

reservoirs.  Similar  specialization  of  parts  of  lower  plants 
occurs.  Carbohydrates  are  sometimes  transformed  into  fats 
for  storage  purposes,  but  carbo- 
hydrate and  proteid  reserve  food 
is  usually  solid.  Reserve  car- 
bohydrates usually  occur  in  the 
form  of  starch,  sugar,  cellulose, 
gum,  etc.  Reserve  proteids  are 
usually  in  the  form  of  aleurone 
grains.  The  starch  is  deposited  in 
the  form  of  large  rounded  or  oval 
grains  (sphere-crystals),  which  often 

.  .   .        Fig.  175.— Aleurone  (proteid)  grains. 

shOW  layers  0\  dillcivnt  composition      /.  from  seed  oi  peony.    ■>.  to,,,, 

the  outer,    /'.   from   the   middle,   c, 
and   density    (fig.     I74).         FatS  OCCUr       from    the    inner    layers.      //,    from 

.       seed  of  castor  bean     a,  in  alcohol ; 
in    liquid    form   as   droplets   of  van-     b,  after  treatment  with  iodine  solu- 
tion and  alcohol.     In  both,  f,  elo- 

ous  size,  and  are  only  rarely  solid,     boid;  <■.  crystalloid.    Very  highly 

magnified. — After  Zimmermann. 

Aleurone  grains  are  really  vacuoles 

filled  with   reserve    proteids.      Some    of  the    proteids  often 


17°  PLANT  LIFE. 

crystallize  |  producing  a  crystalloid),  and  other  materials  are 
frequently  present,  which  form  the  globoid  (fig.   175). 

237.  Intracellular  digestion. — When  solid  foods,  insol- 
uble in  water,  are  to  be  moved  from  one  part  of  the  plant  to 
another  it  must  be  done  by  altering  them  into  soluble  sub- 
stances. This  is  accomplished  by  means  of  enzymes  of  differ- 
ent kinds,  adapted  to  effect  the  alteration  of  various  foods. 
The  most  abundant  enzyme  is  diastase,  which  has  the  power 
of  altering  starch  into  a  sugar  called  maltose.  Enzymes  fitted 
to  transform  proteids  are  also  found  in  considerable  amounts. 
When  the  foods  have  thus  been  brought  into  a  soluble  condi- 
tion, they  dissolve  in  the  water  present  and  move  from  one 
part  of  the  plant  to  another,  chiefly  by  osmosis.  As  any 
given  material  is  used  up  in  growth  or  repair,  or  is  altered 
into  another  substance,  a  constant  stream  of  molecules  of 
this  material  moves  toward  the  point  at  which  it  is  disappear- 
ing. Thus  from  the  food  sources  it  is  transferred  to  the 
reservoirs  and  stored  in  suitable  form.  Thence,  when  needed, 
it  is  redissolved  after  digestion  and  carried  to  the  active  parts 
which  utilize  it. 


F.     Katabolism. 

238.  Destructive  changes. — Coincident  with  the  processes 
which  result  in  the  formation  of  complex  organic  substance 
out  of  simpler  ones  are  those  which  result  in  its  destruction. 
The  constructive  processes  are  grouped  under  the  term  anab- 
n/i.xm,  and  the  destructive  ones  are  designated  as  katabolism. 
In  the  green  plants  the  anabolic  changes  predominate  (be- 
cause of  extensive  photosyntax),  with  the  result  that  the  plant 
accumulates  organic  matter ;  while  in  colorless  plants  kata- 
bolic  processes  predominate,  with  the  result  that  the  plant 
increases  in  bulk,  but  only  at  the  expense  of  organic  materials 
previously  existent.      In  all  plants,  however,  both  the  con- 


NUTRITION.  17 l 

structive  and  destructive  changes  go  on  at   the  same   time 
and  without  conflict. 

239.  Respiration. — A  series  of  katabolic  changes  is  in- 
cluded under  the  term  respiration.  It  is  a  familiar  fact  that 
the  higher  animals  cannot  live  without  a  constant  supply  of 
oxygen  and  a  corresponding  excretion  of  carbon  dioxide. 
This  is  not  so  generally  known  to  be  true  of  plants.  It  is, 
nevertheless,  true  that  no  plant  can  live  without  a  constant 
supply  of  oxygen  and  a  corresponding  excretion  of  carbon 
dioxide.  The  processes  by  which  oxygen  is  obtained  and 
carbon  dioxide  excreted  constitute  respiration. 

240.  Respiratory  ratio. — The  ratio  between  the  amount 
of  oxygen  consumed  and  carbon  dioxide  produced  varies 
somewhat  with  the  age  and  condition  of  the  plant,  as  well  as 
with  the  circumstances  under  which  respiration  occurs. 
Ordinarily  the  volume  of  carbon  dioxide  produced  is  approx- 
imately equal   to  the  volume   of  oxygen   consumed,  and   the 

ratio  may  be  expressed  thus:    -—  —  1. 

241.  Respiration  and  photosyntax. — In  the  green  plants 
respiration  is  masked  in  daylight  by  photosyntax.  When- 
ever the  green  parts  are  sufficiently  illuminated,  the  carbon 
dioxide  produced  by  their  respiration  is  consumed  in  the 
formation  of  carbohydrates  for  food,  lint  when  these  parts 
are  not  adequately  illuminated,  the  process  of  photosyntax 
is  interrupted,  and  respiration  can  be  studied.  The  parts 
of  plants  which  are  free  from  chlorophyll,  such  as  young 
flowers,  buds,  embryos,  and  the  like,  and  all  the  non-green 
plants,  allow  the  respiratory  changes  to  be  demonstrated 
readily. 

242.  Aeration. — The  oxygen  consumed  comes  from  the 
atmosphere,  or  from  the  molecules  of  this  gas  dissolved  in 
water.  Certain  plants  are  adapted  to  aerial  respiration,  while 
others  are  adapted  to  aquatic   respiration,  but   in   either  case 


172  PLANT   LIFE. 

the  gas  used  is  the  same.  In  the  smaller  and  simpler  plants 
the  protoplasm  absorbs  oxygen  directly  through  the  cell  wall. 
In  multicellular  plants,  however,  especially  when  these  be- 
come large  and  complex,  only  the  superficial  cells  could  do 
this.  The  internal  cells  are  too  far  from  the  source  of  supply 
to  allow  an  adequate  amount  of  oxygen  to  reach  them  by 
osmosis  through  other  cells.  In  large  plants,  therefore, 
intercellular  spaces  are  provided,  communicating  with  the 
external  air,  and  through  these  oxygen  diffuses.  In  the 
land  plants  the  intercellular  spaces  are  continued  through  the 
epidermis,  in  which,  with  the  guard  cells,  they  constitute 
the  stomata  (•[  166).  On  the  older  parts  of  woody  plants 
which  have  begun  to  form  a  periderm  the  stomata  are  replaced 
by  lenticels,  through  which  the  internal  intercellular  spaces 
communicate  with  the  outer  air  (^[  140).  In  the  absence  of 
stomata  or  lenticels,  however,  the  oxygen  may  pass  through 
any  part  of  the  surface  of  the  plant.  In  submerged  water 
plants,  very  large  intercellular  spaces  are  formed  (fig.  117), 
permitting  the  existence  of  an  internal  atmosphere  of  con- 
siderable amount,  within  whose  limits  gaseous  exchanges  may 
occur.  Oxygen  may  reach  these  intercellular  spaces  from 
the  water  through  the  superficial  cells. 

243.  Intramolecular  respiration. — While  free  oxygen  is 
ordinarily  utilized  for  respiration,  all  plants  seem  to  be 
capable  of  obtaining  their  supply  for  a  short  time  from  the 
organic  matter  of  the  plant  itself.  Such  respiration  has  there- 
fore been  called  intramolecular  respiration.  It  can  exist  at 
most  for  a  few  hours  without  producing  disease  and,  sooner 
or  later,  the  death  of  the  plant.  It  is  precisely  parallel  to 
the  similar  method  of  respiration  possible  among  cold-blooded 
animals.  A  few  plants  of  the  simpler  sort,  such  as  the 
bacteria,  rely  wholly  upon  combined  oxygen  for  their  respira- 
tory supply.  Such  plants  have  adapted  themselves  to  grow 
in  the  absence  of  free  oxygen,  which,  instead  of  facilitating 


NUTRITION.  1/3 

their  life  processes,  really  checks  them.      They  are  known  as 
anaerobic  plants. 

244.  Excretion. — The  carbon  dioxide  produced  by  res- 
piration, when  not  used  for  photosyntax,  is  gotten  rid  of  by 
the  reverse  of  the  methods  described  for  the  absorption  of 
oxygen. 

245.  Release  of  energy. — The  purpose  of  respiration  is 
to  set  free  energy  required  for  growth  and  movement.  While 
plants  are  capable  of  utilizing  radiant  energy  of  the  sun  for 
photosyntax,  they  must  set  free  within  their  own  bodies  the 
energy  requisite  for  putting  in  place  particles  of  new  material 
to  form  new  parts,  and  for  the  execution  of  movements, 
whether  internal,  such  as  the  streaming  or  rotation  of  the 
protoplasm,  or  mass  movements,  such  as  those  of  leaves  and 
other  members,  or  movements  of  locomotion,  such  as  those 
of  swarm  pores  and  sperm  cells.  (See  ^|  276  ff.)  The  re- 
quired energy  is  set  free  by  the  decomposition  of  organic 
matter. 

246.  Loss  of  weight. — As  a  consequence  there  ensues  a 
loss  of  weight.  If  a  plant,  such  as  a  seedling  abundantly 
supplied  with  reserve  food,  be  compelled  to  develop  in  dark- 
ness, and  so  allowed  to  make  no  additional  food,  it  may  be 
easily  demonstrated  that  a  large  part,  often  as  much  as  one 
half,  of  its  weight  will  be  lost  (as  gases)  in  respiration.  This 
loss  of  weight  conies  primarily  from  the  decomposition  of 
portions  of  the  living  protoplasm.  These,  however,  are  soon 
replaced  by  the  formation  of  new  protoplasm  from  the  pro- 
teids,  and  these  again  are  replaced,  as  already  described,  by 
the  use  of  carbohydrates  and  nitrogenous  compounds.  Ulti- 
mately, therefore,  respiration  results  in  a  diminution  of  the 
reserve  food,  especially  of  the  carbohydrates. 

247.  A  vital  function. — Respiration  is  a  function  of  the 
protoplasm,  and  does  not  occur  simply  because  oxidizable 
substances  are   present  in   the   plant   and   oxygen   is  brought 


1^4  PLANT  LIFE. 

into  contact  with  them.  On  the  contrary,  the  oxygen  seems 
to  enter  into  loose  combination  with  protoplasm,  forming 
an  extremely  unstable  compound  which  under  unknown  con- 
ditions breaks  down  into  simpler  substances,  setting  free 
energy.  Some  of  these  materials  are  again  used  in  building 
protoplasm,  while  others  break  down  still  further,  ultimately 
into  water  and  carbon  dioxide.  The  supply  of  oxygen  is  so 
necessary  that  if  a  plant  cannot  obtain  oxygen  from  without, 
it  will  secure  it  by  the  destruction  of  part  of  its  own  sub- 
stance for  a  time,  as  shown  by  intramolecular  respiration. 

248.  Heat. — While  this  decomposition  of  the  protoplasm 
in  ordinary  respiration  is  not  a  true  oxidation,  it  nevertheless 
results,  as  oxidation  does,  in  the  evolution  of  heat.  The 
amount  of  heat  produced  is  usually  not  great  enough,  and  its 
loss  too  rapid,  to  make  it  readily  perceptible.  Anything 
which  prevents  the  radiation  of  heat  will  make  its  measure- 
ment possible.  The  germination  of  large  quantities  of  seeds 
or  the  blossoming  of  a  number  of  flowers  in  a  confined  space 
may  raise  the  temperature  as  much  as  15  or  200  above  that 
of  the  air.  The  heating  of  hay,  grain,  and  similar  substances, 
which  have  been  stored  when  moist,  is  due  partly  to  the 
respiratory  activity  of  bacteria  and  fungi,  which  grow  rapidly 
under  these  conditions.  Fermentative  changes,  which  also 
occur  under  the  same  conditions,  add  to  the  evolution  of 
heat. 

249.  Light. — A  few  plants  also  produce  light.  This  light 
is  like  that  seen  when  phosphorus  is  exposed  to  the  air  in 
darkness,  or  when  the  end  of  a  match  is  lightly  rubbed. 
Phosphorescence  occurs  only  in  some  bacteria  and  fungi. 
When  it  is  seen  upon  decaying  meat,  fish,  or  wood,  it  is 
because  these  organisms  are  present.  It  does  not  arise  from 
the  decaying  substance  itself.  Several  of  the  larger  fungi,  as 
certain  toadstools,  have  a  mycelium  capable  of  emitting  this 
phosphorescent  light. 


NUTRITION.  1/5 

250.  Contrast  between  respiration  and  photosyntax. — 
Since  the  processes  of  respiration  and  photosyntax  in  green 
plants  are  so  frequently  confused,  a  contrast  is  here  drawn 
between  them. 

Respiration.  Photosyntax. 

Occurs  in  all  living  cells.  Occurs  only  in  green  cells. 
Indifferent   to  or  retarded  by      Requires  light. 

light. 

Consumes  organic  matter.  Produces  organic  matter. 

Produces  carbon  dioxide.  Consumes  carbon  dioxide. 

Consumes  oxygen.  Produces  oxygen. 

Sets  free  energy.  Accumulates  energy. 

251.  Other  katabolic  changes. — Besides  those  constitut- 
ing respiration,  a  considerable  number  of  other  katabolic 
changes  occurr,  which  are  not  so  closely  connected  with 
the  vital  functions  of  the  plant.  They  result  in  the  produc- 
tion of  substances  which  are  of  no  further  use  in  nutrition 
and  only  of  incidental  value  for  any  purpose.  Such  sub- 
stances may  be  stored  in  some  out  of  the  way  place,  or  in 
such  parts  as  are  transient,  and  by  the  loss  of  these  parts  the 
useless  materials  are  gotten  rid  of  J  or  they  may  be  excreted 
directly.  The  waste  materials  are  either  nitrogenous  or 
non-nitrogenous. 

252.  Non-nitrogenous  by-products. — Among  the  non- 
nitrogenous  materials  the  most  important  are  the  carbon 
acids.  su<  h  as  oxalic,  malic,  etc.,  the  tannins,  the  resins,  the 
gums  and  the  volatile  oils.  These  substances  are  either  by- 
products of  photosyntax,  or  they  arise  in  the  course  of  the 
assimilation  of  foods.  Oxalic  acid  is  usually  gotten  rid  of  by 
being  combined  with  lime  to  form  calcic  oxalate,  which 
crystallizes  either  in  the  form  of  squarish  crystals  or  as  long 
needles,  the    form    depending   upon    the   amount  of  water  of 


1 76 


PLANT  LIFE. 


crystallization   (fig.  176).     The  resins,  usually  dissolved  in 
an  oil,  are  generally  exereted  into  special  intercellular  spaces 


Fig.  176.  Crystals  found  in  plants.  I,  calcium  carbonate;  II-V,  calcium  oxalate; 
II,  octahedron  with  blunt  ends;  III,  compound  crystals  from  the  nectary  of  a  mallow; 
IV,  ,i,  /■,  needle  crystals  (raphides)  from  leaf  of  fuchsia  ;  V,  cell  from  the  fruit-Mesh 
of  a  rose  showing  a  crystal,  k,  embedded  in  an  outgrowth  of  the  cell-wall, .  .  All  highly 
magnified. — After  Behrens. 


(fig.    17  7)- 


Volatile  oils  are  secreted  by  glandular  hairs 
(c,  fig.  113);  or  are  formed 
in  the  epidermis  itself,  as  in 
flowers  ;  or  are  produced  in 
chambers  near  the  surface, 
the  cells  which  produce  the 
oil  being  disorganized  to 
form    the    cavity    in    which 

Fig.    [77. — Transverse    section    of    an   inter- 
cellular receptacle  for  gum-resin  from  the    the     drops     lie     (fig.      17^)- 
fruit   of   fennel.       The   secretion   has   been 

dissolved  out  by  alcohol.     The  shaded  cells    Other      materials,      SUCh      !1S 
lining   the    tube   are    the    secretory   tissue. 
Moderately  magnified.— After Tschirch.  salts  of   lime,   arc  sometimes 

excreted  upon  the  surface  of  the  plant.  From  glands  in 
the  flower,  nectar,  which  is  a  solution  of  sugar,  is  excreted 
(figs.  179,  180).  The  loss  of  this  food  is  compensated  for 
by  its  attractiveness  for  insects,  which  incidentally  serve  for 
the  transfer  of  pollen   from   one   flower  to  another.      Caout- 


NUTRITION. 


177 


chouc  and  gutta-percha  occur  in   the  milky  juice  of  certain 
plants. 

253.   Nitrogenous  by-products. — Among  the  nitrogenous 
waste  materials  the  most  important  are  the  alkaloids,  such  as 


Fir..  178.— Section  through  oil-receptacles  in  rind  of  orange,  a,  structure  at  the  beginning 
of  the  disorganization  of  the  oil-producing  cells;  />,  final  condition,  with  two  drops  of 
oil  occupying  the  cavity.     Moderately  magnified. —After  Tschirch. 


Fig 


Fig.  180. 

d  surface  of  the  cup,  >/, 


Fig.  179. — A  flower  of  the  red  currant  cut  in  half.     The  rouglu 

secretes  nectar.     Magnified  5  diam.— After  Kerner. 
In..  180.     I,  ,1  petal  from  the  flower  ol  a  buttercup  {Ranunculus  acris),  showing  the 

nectary,   n.     Magnified  3  diam.     II,  diagram  of  a  longitudinal  section  ol  tin-  same 

through  the  nectary   //.     The  tissue  lining  the  pouch  of  the  petal,  b,  secretes  the  drop 

of  nectar,  /.     Magnified  8  diam.     After  Behrens. 

quinine,  morphine,  strychnine,  nicotine,  etc.,  which  occur  in 
the  seeds,  bark,  or  leaves,  and  are  gotten  rid  of  when  these 
are  dropped. 


CHAPTER  XIV. 

GROWTH. 

254.  Definition. — The  growth  of  plants  is  continued  for 
a  much  longer  time  than  that  of  animals.  In  most  cases  it 
is  continued  in  some  part  throughout  the  existence  of  the 
plant.  There  are  also  changes  in  the  form  of  certain  parts, 
particularly  of  the  lower  plants,  which  must  be  distinguished 
from  true  growth.  Growth  is  a  permanent  change  of  form 
accompanied  usually  by  an  increase  in  size. 

255.  Formation  of  new  parts. — Each  new  cell  originates 
in  the  division  of  some  previously  existing  cell  by  a  partition- 
wall.*  The  two  cells  so  formed  grow  until  they  attain  the 
size  of  the  parent  cell,  when  one  or  both  may  continue  to 
grow  until  they  attain  a  permanent  form;  then  growth  ceases. 
Those  cells  which  do  not  develop  into  permanent  tissue,  but 
retain  their  power  of  division,  constitute  a  mass  of  tissue  at 
the  tip  of  each  branch  or  root,  the  primary  meristem  (^[  77, 
101).  Permanent  tissue  which  resumes  active  division  is 
called  secondary  meristem  (^[  86,  134).  It  will  be  seen, 
therefore,  that  every  cell  of  a  plant  has  been  at  some  time  in 
an  undeveloped  or  embryonal  condition. 

256.  Phases  of  cell  development. — The  characteristics  of 
this  embryonal  condition  are  the  nearly  uniform  and  small 
size  of  the  cells,  the  relatively  large  nuclei,  and  the  absence 
or  small  size  of  the  vacuoles  (A,  fig.  181).  As  the  cells  which 
are  destined    to   become   the   permanent   tissues  grow   older 

*  To  this  there  are  only  unimportant  exceptions. 

17S 


GROWTH. 


179 


they  pass  gradually  from  the  embryonal  stage  into  a  second 
phase  of  development,  the  stage  of  elongation.  This  stage  is 
marked  by  the  rapid  Increase  of  the  cells  in  size  and  a  much 
less  marked  increase  in  the  mass  of  protoplasm  present.  In 
order  to  maintain  the  turgor  of  the  cells,  there  is  a  great  in- 
crease in  the  volume  of  water,  which  accumulates  in  one  or 


Fig.  [81. — Cells  from  young  and  mature  fruit  of  snowberry  (Symthoricarpui),  seen  in 
section.  ./,  three  young  cells,  very  small,  walls  thin,  inn  lei  relatively  large,  vacuoles 
very  minute;  />',  two,  somewhat  older ;  larger,  walls  thicker,  nuclei  smaller,  vacuoles 


several.  A  and  />'  magnified  300  diam.  C,  a  single  cell,  mature,  magnified 
di.1111..  inie  third  as  much  as  .  /  and  A'.-  vacuole  single,  very  large.  The  volume  ol 
<  is  more  than  1500  times  one  of  the  cells  in  A  .  h ,  cell-wall  ;  p,  protoplasm  ;  <<•,  nu- 
cleus; kk,  nucleolus;  s,  vacuole. — After  l'rantl. 

more  large  vacuoles  ((",  fig.  t8i  ).  If  the  organ  in  question 
has  an  elongated  form,  such  as  the  stem  or  the  root,  growth  of 
the  cells  takes  place  chiefly  in  the  direction  of  its  long  axis, 
although  an  increase  also  occurs  in  the  transverse  directions. 
During  this  phase  the  tells  may  attain  a  hundred  or  even  a 
thousand  times  their   former  volume.      Growth  in  length  can 


180  PLANT  LIFE. 

be  studied  by  direct  observation  with  a  microscope,  but  more 
<  onveniently  by  magnify  ing  the  growth  by  mechanical  means, 
so  as  to  observe  the  movements  of  a  pointer  over  a  scale. 
Such  an  instrument  is  an  auxanometer.  Those  forms  of  it 
which  secure  a  continuous   record  automatically  are  of  the 


Fig.  182. — Golden's  auxanometer.  The  instrument  1  onsists  of  two  parts,  a  multiplying 
pulley  and  two  recording  rods  turned  by  a  clock.  V  thread  from  the  plant  passes 
through  a  bent  glass  ,U',L'  ,llu'  makes  one  turn  around  the  small  pulley  to  which  it  is 
then  f.isti-iu-d.  Another  thread  makes  one  turn  around  large  pulley  and  descends 
to  carry  a  pointer  which  slides  on  two  guide  rods.  Asthe  plant  grows  the  thread 
from  it  slackens  and  the  pointer  descends  at  a  magnified  rate  by  its  own  weight.  Two 
glass  rods,  blackened  in  a  smoky  gas-flame,  are  rotated  by  a  clock  to  whose  hour 
spindle  the  frame  carrying  them  is  atta<  hed.  Vs  thl  \  pass  the  pointer  a  mark  is  made 
on  the  smoked  sulfate.  The  distance  id  the  suciessive  marks  shows  the  amount  of 
growth  as  magnified.  Permanent  record  may  lie  made  by  means  of  blue  prints,  using 
the  rods  (which  are  removable)  as  negatives.— After  Arthur. 

most  service  (fig.  182).      By  imperceptible  gradations  these 

cells  pass  into   the  third  and  final  stage  of  growth,  which  is 


GROWTH. 


i8i 


characterized  by  permanent  and  usually  irregular  thickenings 
of  the  wall  (figs.  10,  n,  52,  58). 

257.  Grand  period  of  growth. —  The  entire  duration  of 
growth  of  an  organ  is  known  as  its  grand  period  of  growth. 
Corresponding  precisely  to  the  phases  in  cell  development, 
there  are  three  phases  in  the  development  of  the  organ  as  a 
whole.  Its  growth  is  at  first  very  slow,  increasing  gradually, 
and  then  more  rapidly,  to  a  maximum,  from  which  it  falls 
rapidly,  and  then  more  gradually,  until  it  ceases  entirely.  The 
earliest  phase,  the  embryonal,  results  in  so  little  elongation 
that  it  is  scarcely  possible  to  have  it  recorded  by  the  auxanom- 
eter.     The  last  phase,  that  of  internal  differentiation,  is  not 


2V 

I  \ 

t       v 

4          \ 

/             \ 

S           IX 

/            V 

t             S 

4                  s^ 

L                                 ^ 

^                                         s^ 

0            4             8            13           16           80 

Fig.  183. — Curve  representing  the  rate  of  growth  of  an  internode  >>f  crown  imperial  tor 
each  day  during  the  grand  period — in  this  rase  _'*.  days.  The  height  ol  each  \  ertical  line 
where  it  intersects  the  curve  represents  the  total  growth  for  the  corresponding  24 
hours.  The  numbers  indicate  days.  The  maximum  growth  occurred  on  the  6th  day. 
—  After  Sadis. 


marked  by  any  elongation.  The  accompanying  curve  (fig. 
[83)  therefore  represents  only  the  duration  and  course  of  the 
phase  of  elongation. 

258.  Growing  region.— The  part  of  any  one  of  the  multi- 
cellular plants,  which  is  growing  in  length,  is  limited.  The 
elongating  region  of  a  root  rarely  exceeds  a  centimeter,  and 
is  often  not  more  than  one  halt  a  centimeter  in  length.      In 


182 


PLANT  LIFE. 


stems,  however,  the  elongating  part  may  measure  twentyoreven 

fifty  centimeters,  and  in  rare  cases 
much  more.  Figure  184  shows  a 
root,  A,  upon  whose  surface  marks 
were  made  1  111111.  apart.  Twenty- 
four  hours  later  the  root  presents 
the  appearance  of  B.  Only  the 
tissues  in  the  first  five  spaces  were 
capable  of  elongation.  The  others 
had  passed  into  the  third  phase. 
The  second  and  third  millimeters 
grew  most  in  length.  The  growing 
regions  of  stems  may  be  deter- 
mined in  the  same  way. 

259.  Tension  of  tissues. — The 
different  tissues  in  any  organ  usu- 
ally do  not  grow  at  an  equal  pace, 
and  consequently  certain  tissues 
are  under  strain,  while  others  are 
compressed.  The  curled  and 
crinkled  leaves  or  the  curved  cap- 
sules of  mosses   illustrate   this  in- 


marked  with  fine  lines  of  Chinese  equality.    It  maybe  present,  how- 

ink  into   13  spaces  of   i   millimeter        l  J  J  * 

each.     /:,  the  same  root,   24  hours   ever     without  manifesting    itSt'lf  ill 

later,    showing    elongation    only   in  '  ° 

terminal  5  millimeters      The  rate  of    external   form.         This   general   COn- 
growth  is  greatest   m  the  2d  and  3d  ° 
millimeters  and  slow  in  the  ,s,,,h.     (1J,K)U    jg     kllOWliaS     1 1 1 C   /etlSlOfl     of 
and  i\\\.      .Magnified  1  chain. —Alter 

Prank. 


/issues.  If  the  rapidly  growing 
flower-stalk  of  the  dandelion  or  the  leafstalk  of  rhubarb 
be  carefully  split  lengthwise  the  parts  will  curve  or  even  curl 
outward.  Separating  the  inner  and  outer  tissues  of  a  young 
elder  shoot  and  carefully  measuring  them  shows  that  tin- 
inner  tissues  elongate  and  the  outer  actually  shorten.  The 
experiment,  therefore,  shows  that  the  inner  tissues  really 
grew  more  rapidly  than  the   outer,  but   were  compressed   in 


GROWTH.  183 

the  uncut  stem,  while  the  outer  ones  were  slightly  stretched. 
The  strains  thus  set  up  are  spoken  of  as  longitudinal  tissue 
tensions.  Similar  tensions  due  to  unequal  transverse  growth 
may  be  shown  to  exist.  If  a  thin  transverse  slice  from  the 
fleshy  leaf-stalk  of  the  rhubarb  be  divided  into  equal  parts  by 
a  longitudinal  cut  it  will  be  found  in  a  few  moments  that  the 
halves  can  no  longer  be  made  to  touch  throughout  the  line  of 
the  cut,  because  it  has  become  convex.  Both  the  longitudi- 
nal.and  transverse  tensions  may  be  exaggerated  if  the  parts 
be  placed  for  a  few  moments  in  water. 

260.  Conditions  of  growth. — That  plants  may  grow  cer- 
tain conditions  are  prerequisite.  (1)  There  must  be  an  ade- 
quate supply  of  constructive  materials.  These  may  be  derived 
either  from  food  recently  manufactured  or  from  that  stored 
in  reservoirs,  or,  in  the  case  of  the  colorless  plants,  from  that 
absorbed  from  without.  (2)  There  must  be  a  supply  0/  oxy- 
gen for  respiration.  This  is  needed,  as  previously  explained, 
to  set  free  the  energy  necessary  for  growth.  (3)  There  must 
be  a  supply  of  water  adequate  to  maintain  a  minimum  turgor 
of  the  cells,  without  which  growth  cannot  take  place.  (4) 
A  suitable  temperature  is  required.  The  range  of  temperature 
within  which  growth  may  take  place  is  extensive,  and  varies 
with  the  individual  plant.  In  general,  the  upper  limit  may 
be  stated  as  about  400  C,  and  the  lower,  about  o°  C.  The 
minimum  of  plants  of  tropical  regions  is  approximately  io°  C, 
while  the  maximum  for  plants  of  the  arctic  or  alpine  regions 
is  much  below  400  C.  Between  the  maximum  and  minimum 
temperatures  there  is  an  optimum  temperature  for  each  plant, 
at  which  growth  takes  place  most  rapidly.  For  most  plants 
the  optimum  lies  between  25"  and  320  ('. 

261.  External  conditions  exercise  a  very  important  in- 
fluence upon  the  rate  or  character  of  growth  by  reason  of  the 
irritability  of  the  protoplasm.  (See  further-  418.)  Many 
of  these  conditions  act  upon  members  of  the  plant  so  as  either 


1 84  PLANT   LIFE, 

to  bring  about  permanently  unequal  growth  in  a  certain  part, 
or  to  cause  one  part  to  grow  more  or  less  rapidly  for  a  time 
than  another.  Such  variations  in  growth  produce  curvatures 
in  the  parts  concerned  and  move  members  connected  with 
them.  They  are  therefore  discussed  in  the  chapter  on  Move- 
ments. Those  conditions  which  act  more  generally  and 
uniformly  upon  a  large  number  of  plants  have  a  tonic  eflfei  t 
and  serve  to  determine  the  form  and  mode  of  development  of 
members. 

262.   Light. — The   tonic   effect  of  light   is  different   upon 
different  plants  and  even  different  members  of  the  same  plant. 


\ 


A 


Fig.  1S5. — Part  of  the  transverse  sections  of  the  stem  of  rye.  .  I.  From  a  plant  grown 
fully  exposed  to  light;  /■'.  from  a  "laid"  plant  imperfectly  exposed  to  light,  n , 
epidermis;  b,  c,  mechanical  tissues;  </,  thin-walled  tissues.  Highly  magnified.— After 
Koch. 

In  general  light  retards  growth  in  length.  Stems  grown  in 
darkness  usually  become  excessively  elongated.  Those 
which     under     normal     illumination     have     internodes    very 


GROW  TIL 


I85 


short,  in  diminished  light  may  have  them  well  developed,  as 
occurs,  for  example,  in  dandelions  growing  in  deep  shade. 

In  general,  light  accelerates  the  growth  of  leaves  in  area. 
Leaves  of  shoots  grown  in  darkness  remain  small. 

Light  affects  not  only  the  external  form  but  the  internal 
structure.  In  diminished  light  the  cell  walls  do  not  thicken 
normally,  and  mechanical  tissues  are  weakened.  "  Laying" 
of  oats  and  such  grasses  is  mainly  due  to  this  cause  (fig.  185). 
In  weak  illumination  the  palisade  tissue  of  the  leaves  (%  167) 
is  poorly  developed. 

263.  Light  and  temperature. — The  combined  variation 
of  light  and  temperature  between  day  and  night  establishes  a 
daily  period  in  the  growth  of  all  plants.  The  withdrawal  of 
light  at  night  permits  an  increase  in  the  rate  of  growth  in 
length,  which  reaches  its  maximum  in  some  plants  shortly 
after  midnight,  in  others  not  until  the  early  morning.  During 
the  day  its  retarding  effect  diminishes  the  rate  of  growth, 
which  reaches  a  minimum  some  time  in  the  afternoon.      The 


5   ;   ■■)  11  1    3   5   7  y  11  1   s  5   7  a  11  1 

N  M  N 

Fir..  186.— Curve  showing  the  daily  period  in  the  growth  of  a  stem  of  rye.  The  vertical 
lines  represent  2-hour  periods  from  5  P.M.  of  one  day  to  5  a.m.  of  the  second  day. 
the  shaded  parts  indicating  the  actual  hours  of  darkness.  The  horizontal  lines  repre- 
sent tenths  of  a  millimeter.  The  curve  is  drawn  by  taking  the  record  from  an  aux- 
anometer  and  laying  off  on  the  vertical  line  For  each  interval  the  growth  shown,  The 
points  arc  then    joined.     It  will  be  observed  that  the  maximum  rate  ol  growth 

shortly  after  the  period   ol   darkness  (5  A.W    I  and   the  minimum  rate  alter  the  period  of 
most  intense   illumination   (5  P.M.).      During   the   experiment   the  thermometer  varied 

from  [8°  to  220  C. — After  Frank. 


minor   fluctuations   in    temperature,  as  well   as   the   generally 
higher  temperature  during  the  day  and  lower  during  the  night, 


186 


PLANT   LIFE. 


introduce  variations  in  the  rate  of  growth,  which  obscure,  but 
do  not  counteract,  the  retarding  influence  of  light.  (See  fig. 
186. )  This  daily  period  is  so  impressed  upon  the  constitu- 
tion of  the  plant  that  it  maintains  it  for  a  considerable  time 
even  when  kept  in  complete  darkness.  Stems  of  sunflower, 
after  two  weeks  in  complete  darkness,  still  showed  distinctly 
the  daily  period.  A  similar  daily  period  is  apparent  in 
the  tension  of  tissues  which  depends 
on  growth. 

264.  Moisture  and  oxygen. — The 
amount  of  moisture  and  oxygen  pres- 
ent in  the  medium  surrounding  a 
plant  profoundly  affects  its  form. 
Amphibious  plants,  that  is,  those 
which  are  capable  of  growing  either 
on  land  or  in  water,  often  show  this 

Fig.  187.  — a  shoot  of  water  in  a  striking  way.      When  grown  sub- 
crowfoot     {Ranunculus  ,       ,       . 
aquatuis).  The  lower  leaves  merged,   the  leaves  are  usually  finely 

have   developed  under  water  .  , 

and  are  branched  into  many  divided,      while      the 

narrow     divisions;     the     two 

upper  leaves  have  developed  allowed     to     develop 

in    air   and    at    maturity    float 

on  the  surface    of  the  water,   broad  blades  Scarcely 

About    half    natural    size.  — 

After  Frank.  (fig-    187). 


same  leaves,  if 
in  the  air,  have 
more  than  lobed 


265.  Mechanical  pressures  or  strains  also  exert  an  in- 
fluence upon  the  rate  and  mode  of  growth.  Compression  of 
tissues  retards  their  growth;  strains  accelerate  it.  Thus, 
stems  enclosed  in  plaster  casts  or  ligatured  grow  more  slowly 
in  thickness.  Tensile  strains,  such  as  those  exerted  by  wind 
or  weight,  promote  the  development  of  mechanical  tissues. 
Petioles,  which  would  break  under  a  strain  of  700  gm.,  after 
enduring  a  pull  of  500  gm.  for  five  days,  broke  only  at  1600 
gm.  Alter  five  days  more  under  a  strain  of  1200  gm.  they 
could  not  be  broken  with  less  than  a  weight  of  6500  gm. 

266.  Variations  in  rate. — There  are  not  only  variations 
in  growth  in  the  course  of  each  day  throughout  the  growing 


growth.  187 

period,  but  also  minor  variations  independent,  so  far  as 
known,  of  external  conditions,  which  are  therefore  called 
spontaneous  variations.  Irregular  variations  occur  from  hour 
to  hour  in  the  course  of  the  day.  Regular  spontaneous 
variations,  also,  occur  in  various  organs,  particularly  in  the 
tendrils  of  climbing  plants,  and  in  the  leaves  of  flowers  and 
buds.  These  regular  variations,  which  affect  different  sides 
of  bilateral  organs  and  different  sectors  of  cylindrical  ones, 
bring  about  a  bending  of  the  entire  organ  from  one  side 
to  another.  These  curvatures  produce  nutation,  and  will 
be  further  described  under  movements.      (See  ^|  283.) 

267.  Duration. — Even  when  the  external  conditions  of 
growth  are  kept  as  uniform  as  possible,  growth  does  not  con- 
tinue for  an  indefinite  time.  Having  passed  through  the 
phases  above  named,  it  ceases,  no  matter  how  favorable  the 
external  conditions.  Yet  some  organs,  even  after  growth 
has  ceased,  may  resume  it,  provided  they  are  affected  by 
suitable  stimuli.  Thus,  the  leaf  cells  which  have  long  since 
ceased  to  divide  may  resume  the  power  of  division  in  the 
neighborhood  of  a  wound,  and  by  division  and  the  growth 
of  new  cells  may  form  a  callus  covering  the  wound.  The 
stimulus  following  fertilization  also  induces  growth  in  parts 
adjacent  to  the  egg,  as  is  most  strikingly  shown  in  the 
formation  of  fruits  of  the  seed  plants.      (See  ^|  404,  409.) 


CHAPTER  XV. 

THE  MOVEMENTS  OF  PLANTS. 

268.  Irritability. — Among  the  fundamental  properties  of 
protoplasm  are  irritability  and  automatism.  We  know  practi- 
cally nothing  of  the  nature  of  either  of  these  properties, 
though  upon  them  depend  all  the  movements  executed  by 
plants.  Automatism  is  the  name  given  to  the  power  in 
virtue  of  which  protoplasm  is  able  to  initiate  internal  changes 
without  the  action  of  any  external  force.  Irritability  ex- 
presses the  power  of  the  protoplasm  to  respond  or  react  to 
the  influence  of  an  external  change. 

269.  Stimuli. — The  external  change  which  brings  about 
the  reaction  is  known  as  a  stimulus,  and  its  application  is 
called  stimulation.  External  forces  which  may  act  as  stimuli 
are  light,  heat,  gravity,  moisture,  electricity,  chemical  sub- 
stances, etc.  Most  of  these  act  constantly  upon  plants.  In 
order  that  they  may  act  as  stimuli,  therefore,  a  relatively 
sudden  change  in  intensity  or  direction  must  occur.  Some- 
times, however,  a  slow  change  will  still  produce  a  reaction. 
For  example,  the  gradual  withdrawal  of  light  may  cause 
movements  of  leaves.      (See  ^[  297.) 

270.  Conditions  limiting  irritability. — Protoplasm  is  ir- 
ritable only  under  certain  conditions,  which  coincide  in  the 
main  with  those  that  promote  the  general  well-being  or  life 
of  the  organism.  The  limits  of  temperature,  moisture,  and 
the  supply  of  oxygen,  which  permit  irritability,  are  much 
narrower  than  those  which  permit  life.  Thus,  irritability 
may  be  lost  when  the  conditions  are  unfavorable,  though  life 


THE    MOVEMENTS    OF  PLANTS.  1 89 

may  persist  under  such  conditions  for  a  long  time.  Irritabil- 
ity may  also  be  lost  through  fatigue,  as  when,  after  repeated 
reaction,  no  response  occurs  to  even  a  greatly  increased 
stimulus.  Upon  the  return  of  suitable  conditions,  or  after 
sufficient  rest,  irritability  may  be  regained. 

271.  Reaction. — The  response  of  the  protoplasm  to  a 
stimulus  is  out  of  all  proportion  to  the  physical  or  chemical 
action  of  the  stimulus  itself.  The  action  of  the  stimulus  upon 
the  irritable  protoplasm  may  be  roughly  compared  to  the 
action  of  the  trigger  niton  a  primed  and  loaded  gun.  It 
sets  free  forces  vastly  in  excess  of  those  which  it  exerts. 

272.  Reaction  time. — The  reaction  does  not  follow  in- 
stantly upon  stimulation.  The  interval,  which  is  known  as 
the  reaction  time,  is  ordinarily  much  longer  in  plants  than  in 
the  higher  animals.  In  extreme  cases  no  reaction  may  be 
manifest  until  several  hours  after  stimulation.  In  other  cases, 
however,  as  in  the  well-known  sensitive  plant,  the  move- 
ments of  the  leaves  follow  almost  instantly  upon  stimulation. 

273.  Form  of  reaction. — The  character  of  the  reaction  is 
not  dependent  upon  the  nature  of  the  stimulus,  but  upon  the 
nature  of  the  organ  itself.  It  is  not  in  the  least  understood 
what  the  inherent  peculiarities  are  which  determine  the  form 
of  the  reaction.  In  different  organs  exactly  opposite  effects 
may  be  produced  by  the  same  stimulus,  and  the  same  organ 
at  different  ages  may  respond  differently  to  the  same  stimulus. 
Thus  the  young  internodes  of  the  Virginia  creeper  {Ampe- 
lopsis)  are  sharply  recurved,  but  become  erect  when  older. 
The  stalk  bearing  the  flower  of  the  peanut  is  erect,  but  as  it 
becomes  older  it  becomes  strongly  retlexed,  and  thrusts  the 
fruit  under  ground. 

274.  Localization  of  irritability. — In  multicellular  plants 
irritability  to  certain  stimuli  is  usually  localized  in  certain 
organs,  and  often  in  special  parts  of  these  organs.  In  many 
tendrils,  for  example,   the   free  end    is  curved  and  only  the 


190  PLANT  LIFE. 

concave  side  is  irritable  to  contact.  In  the  Venus'  fly-trap, 
although  the  whole  leaf  moves  at  the  contact,  only  the  three 
hairs  upon  the  upper  face  of  each  lobe  are  sensitive  to  a 
touch.      (See  figs.  386,  205.) 

275.  Transmission  of  stimuli. — In  these  cases,  as  in  many 
others,  the  effect  of  the  stimulus  must  be  transmitted  in  some 
way  from  the  point  of  application  to  the  cells  which  produce 
movement.  Much  uncertainty  exists  as  to  how  this  is  ac- 
complished. In  some  cases  it  is  doubtless  done  by  means  of 
the  connecting  threads  of  the  protoplasm  from  cell  to  cell, 
after  the  analogy  of  a  diffuse  nerve.  In  other  cases  it  may 
be  transmitted  through  certain  strands  of  tissue  by  the  altera- 
tion of  the  hydrostatic  pressure  in  the  interior  of  the  cells. 

The  movements  of  plants  may  be  conveniently  considered 
as  (1)  movements  of  locomotion  by  single  cells;  (2)  move- 
ments of  protoplasm  within  a  cell-wall;  or  (3)  mass  move- 
ments of  multicellular  members  of  the  higher  plants. 

I.    Locomotion    of   single   cells. 

276.  Naked  cells. — Plants  which  consist  of  a  single  cell 
may  be  either  naked  or  furnished  with  a  cell  wall.  If  naked, 
they  may  exhibit  either  amoeboid  or  ciliary  movements.  Amoe- 
boid movements  are  slow  creeping  movements  brought  about 
by  the  protrusion  of  a  portion  of  the  protoplasm  (a  pseudo- 
podium),  toward  which  the  remainder  gradually  flows  (fig. 
169).  Ciliary  movements  are  due  to  the  extension  of  one  or 
more  very  slender  threads,  called  cilia,  whose  rapid  bending 
in  different  directions  propels  the  organism  (fig.  168). 
According  to  the  nature  of  the  movements,  the  course  will 
be  zigzag  or  steady,  accompanied  by  the  rotation  of  the  cell 
on  its  axis.  When  the  cell  comes  to  rest  the  cilia  are  either 
withdrawn  or  drop  off. 

277.  Cells  with  a  wall. — Movements  of  locomotion  in 
plants  possessed  of  a  cell  wall  are  either  ciliary  or  creeping. 


THE   MOVEMENTS   OF  PLANTS. 


1QI 


The  latter  are  usually  due  to  the  protrusion  of  processes  from 
the  protoplasm  through  slits  in  the  wall,  as  in  many  diatoms 
(fig.  20).  The  filaments  of  the  water  slimes  bend  from  side 
to  side,  and  so  creep  over  wet  surfaces  very  slowly  (fig.  15). 
Bacteria  (fig.  17)  and  some  diatoms  move  by  means  of  cilia. 


V) 

A  1 


II.  Movement  of  protoplasm  within   a  wall. 

278.  Streaming. — In  multicellular  organs  it  is  common 
to  find  the  protoplasm  within  each  active  cell 
moving  about  from  point  to  point  within  the 
cell.  The  protoplasm  is  filled  with  numerous 
large  vacuoles,  so  that  it  forms  a  layer  next  the 
wall,  with  threads  or  ribbons  extending  across 
it  (fig.  188).  When  currents  start  along  the 
wall  and  through  the  strands,  the  motion  is 
designated  as  the  streaming  of  the  protoplasm. 
These  currents  along  any  particular  portion  of 
the  protoplasm  may  run  side  by  side  and  in 
opposite  directions. 

279.  Rotation. — When  the  protoplasm  sur- 
rounds a  single  large  vacuole  and  thus  occupies 
only  the  periphery  of  the  cell  (fig.  181,  C), 
the  whole  mass  may  rotate,  usually  in  the  direc- 
tion of  its  long  axis.  The  portion  immediately 
in  contact  with  the  wall  is  motionless,  and  there 
must  necessarily  be  a  strip  between  the  half  Fie 
moving  up  and  the  half  moving  down  the 
cell,  which  is  also  quiet.  Such  movements  are 
called  rotation  of  the  protoplasm.  It  is  not 
known  whether  either  streaming  or  rotation 
has  any  immediate  relation  to  the  well-being 
of  the  cell. 

280.  Cell  organs. — In  addition  to  the  mass 
movements  of  the  protoplasm,  the  smaller  protoplasmic  bodies 


A  single 
cell  from  a  hair  of 
Chelidonium. 
The  arrows  show 
the  direction  of 
movement  oi  the 
protoplasm  in  the 
peripheral  I  a  y  e  r 
and  in  the  bands 
which  separate  the 
vacuoles,  n,  the 
nucleus,  with  nu- 
cleolus. Highly 
magnified. —  After 
I  lippel. 


192  PLANT  LIFE. 

within  the  cell,  such  as  the  nucleus  and  the  chloroplasts,  are 
capable  of  moving  about.  Under  moderate  illumination 
chloroplasts  accumulate  upon  the  sides  of  the  cells  most  di- 
rectly reached  by  the  light.  Under  very  strong  illumination 
they  retreat  to  the  walls  least  illuminated,  or  may  even  pile 
up  in  the  angles  of  the  cell  so  as  to  shade  each  other  (fig. 
189). 


&At 


Fig.  189. — Cells  from  the  spongy  parenchyma  of  the  leaf  fo  wood  sorrel  {Oxalis),  seen 
from  the  direction  in  which  light  falls  on  the  leaf,  a,  position  of  the  chloroplasts  in 
diffuse  light ;  /',  position  after  short  exposure  to  direct  sunlight ;  c,  position  after  longer 
exposure.     Highly  magnified. — Alter  Staid. 


III.  Movements  of  multicellular  members. 

281.  Forces. — The  movements  of  multicellular  parts  may 
be  brought  about  either  by  special  organs  known  as  motor 
organs,  or  by  the  growth  of  the  immature  parts.  Motor  or- 
gans are  generally  responsible  for  the  movements  of  mature 
[tarts,  while  movements  of  the  younger  regions  are  generally 
due  to  growth.  The  force  exerted  by  the  motor  organs  is 
dependent  upon  the  altered  turgor  of  the  cells  of  which  the 
organ  is  composed.  If  the  cells  upon  one  side  lose  their  tur- 
gidity,  those  upon  the  other,  being  unresisted,  will  extend 
and  bend  the  organ  toward  the  side  upon  which  the  turgor 
was  diminished.  It  will  be  convenient,  therefore,  to  dis- 
tinguish movements  due  to  growth  and  movements  due  to 
variation  in  turgor. 

282.  (A)  Movements  of  growth. — These  depend  upon 
some  inequality  in  the  rate  of  growth  of  the  organ  concerned. 
They  are  of  two  sorts:  (1)  those  in  which  variation  ingrowth 


THE    MOVEMENTS    OF  PL, IX VS.  I93 

is  produced  by  internal  causes,  called  spontaneous  move- 
ments, and  (2)  those  in  which  the  variation  in  growth  results 
from  stimulation  by  external  agents,  called  paratonic  move- 
ments. 

283.  1.  Spontaneous  movements. — Among  spontaneous 
movements  are  those  in  which  the  variation  in  growth  occurs 
upon  different  sides  of  a  cylindrical  organ,  or  the  two  faces  of 
a  bilateral  one.  The  opening  of  all  flower  and  leaf  buds  illus- 
trates this  movement,  which  is  called  nutation.  During  the 
development  of  the  interior  parts,  the  outer  leaves  (often 
scale-like)  which  protect  them  grow  more  rapidly  upon  their 
outer  (dorsal)  surfaces.  They  are  thus  pressed  together  into 
a  compact  bud.  When  the  internal  parts  are  suitably  de- 
veloped a  change  occurs  in  the  rate  of  growth  of  the  outer 
leaves  ;  their  inner  (ventral)  faces  now  grow  more  rapidly 
and  the  bud  expands.  Similar  spontaneous  variation  in  the 
growth  of  different  sides  of  tendrils  produces  a  nodding  or 
waving  motion,  or  even  a  rotation  of  the  tip,  by  means  of 
which  they  are  often  enabled  to  reach  a  support.  In  most 
tendrils  the  acceleration  of  growth  travels  irregularly  around 
the  axis,  so  that  their  tips  rotate  in  a  roughly  circular  or 
elliptical  orbit  from  the  time  the  tendril  is  two-thirds  grown 
until  growth  ceases.  The  further  changes  in  the  tendril,  by 
which  it  wraps  the  tip  about  the  support  and  coils  the  re- 
mainder into  a  double  spiral,  are  paratonic  movements  in- 
duced by  contact.  The  rotating  movements  by  which  twin- 
ing plants  climb  are  also  paratonic  and  not  spontaneous. 

284.  2.  Paratonic  movements  are  also  of  the  highest  im- 
portance for  the  well-being  of  the  plants  concerned.  By  means 
of  them  the  different  organs  are  developed  in  such  situations 
that  they  can  properly  perform  their  work.  The  stimuli 
which  influence  the  rate  of  growth  are  chiefly  light,  gravity, 
heat,  mechanical  contact,  and  moisture.  The  peculiar  states 
in  which  a  plant    or  an    organ   exists  when  it    can  respond  to 


'94 


PLANT  LIFE. 


the  different  stimuli  have  received  different  names,  and  those 
names  indicate  the  nature  of  the  stimulus.  A  plant  or  an 
organ  is  heliotropic  when  it  reacts  to  the  direction  of  the 
rays  of  light  falling  upon  it  ;  geo/ropic,  when  it  reacts  to  the 
force  of  gravity  ;  thermotropic,  when  it  reacts  to  the  presence 
of  a  warm  body ;  hydrotropic,  when  it  reacts  to  the  presence 
of  a  moist  surface,  etc.  In  each  case  the  plants  are  said  to 
react  positively  when  the  movement  is  toward  the  source  of 
the  stimulus  ;  negatively,  when  the  movement  is  away  from 
the  stimulus  ;  transversely,  when  it  is  transverse  to  the  direc- 
tion of  the  stimulus.     These  reactions  are  to  a  certain  extent 


ODD 


Fig.  190. — Diagrams  representing  the  transverse  heliotropism  of  leaves  of  the  garden 
nasturtium  (Tropaolum).  Potted  plants  were  subjected  successively  to  light  strik- 
ing them  in  the  direction  shown  by  arrows.  The  petioles  curved  so  .is  to  place  the 
blades  at  right  angles  to  the  incident  light. — After  VSchting. 

related  to  one  another,  and  it  will  be  convenient,  therefore,  to 
consider  the  effect  of  each  stimulus  upon  the  two  common 
forms  of  plant  organs — namely,  the  radial  (such  as  stems  and 
roots)  and  the  dorsiventral  (such  as  leaves).  Organs  are 
sometimes  physiologically  dorsiventral,  even  though  they 
possess  a  radial  structure  ;  for  example,  some  steins  behave  as 
dorsiventral  organs,  although  they  are  perfectly  radial  in 
structure. 

285.  (a)  Heliotropism. — Heliotropism  is  the  state  of  a  plant 
or  organ  when  it  is  irritable  to  the  direction  of  light  rays. 


THE   MOVEMENTS   OF  PLANTS. 


195 


Light  thus  plays  an  important  part  in  determining  the  position 

of  organs.  As  a  rule  radial  organs  are  either  positively  heli- 
otropic,  as  the  stems  and  leaf-stalks,  or  negatively  heliotropic, 
as  the  roots.  Dorsiventral  organs,  such  as  leaves,  are  all 
transversely  heliotropic,  assuming  a  position  at  right  angles 
to  the  incident  rays,  which  is  the  most  favorable  position 
possible  for  the  manufacture  of  food  by  the  green  parts  (fig. 
190).  Intense  light,  however,  may  bring  about  a  different 
reaction,  so  that  the  leaves  set  themselves  edgewise  to  the 


Fir,.  191. — Leaf  mosaic  formed  by  a  horizontal  shoot  of  Norway  maple.  The  lengthen- 
ing of  the  petioles  of  individual  leaves  to  avoid  shading  of  the  blade  is  marked. 
About  one-third  natural  size. — After  Kerner. 


direction  of  the  rays.  A  fixed  light  position  is  usually 
reached  by  leaves  by  the  time  they  become  mature,  and  this 
is  generally  at  right  angles  to  the  source  of  greatest  light 
branches  of  trees  show  the  leaves  so  arranged  as  to  size  and 
position  that  they  shade  each  other  as  little  as  possible,  form- 
ing the  so-called  leaf  mosaics  (figs.  191  to  193).  The  leaves 
of  window  plants  also  exhibit  these  movements  very  strikingly, 


196 


PLANT   LIFE. 


because  usually  illuminated  from  one  side.      Plants  kept  in 
darkness  have  their  leaves  irregularly  placed. 

286.   (3)   Combined  movements  due  to  variations  in  the 


Fig.  hi2. — A  shoot  of  thorn-apple  or  "  jimson  "  weed,  showing  imperfect  leaf  mosaics 

of  tall  plants  formed  upon  the  same  plan  as  in  rosettes  (fig.  193).   One-seventh  natural 
size. — After  kerner. 

amount  of  light  or  heat  or  both  are  especially  exhibited  by  flow- 
ers,  whose   opening  and  closing  are   frequently   determined 


mw'^M 


V 

Fin.   193. — A  rosette  of  leaves  ol  .1  bellflower  (Campanula  pusilla),  showing  lun^tli- 

ening  of    petioles  of   lower   leaves  so   as  to   tarry  blades   from   under  upper  leaves  — 
After  Kerner. 

thereby.  With  some  plants  the  predominant  stimulus  is  heat; 
with  others,  light.  Closed  flowers  of  the  tulip  or  crocus  may 
be  made  to  open  in  2  to  4  minutes  by  raising  the  temperature 


THE    MOVEMENTS    OF  TLA  NTS.  1 97 

150  to  200.  The  flowers  of  the  white  water-lily  (Nymphaea) 
and  of  the  dandelion  open  in  sunlight  and  (lose  in  shade. 
By  marking  upon  their  leaves  a  series  of  equidistant  parallel 
lines  with  Chinese  ink,  and  subsequently  measuring  the  dis- 
tances to  which  they  have  been  spread,  all  such  movements 
can  be  clearly  shown  to  be  due  to  accelerated  growth  of  the 
outer  or  inner  surfaces,  respectively.  The  protection  of  the 
flower  parts  or  the  proper  discharge  of  the  functions  is  secured 
by  these  movements,  which  must  not  be  confounded  with 
those  due  to  the  direction  of  light  or  heat  rays. 

'287.  (c)  Geotropism. — Geotropism  is  the  state  of  a  plant 
or  an  organ  when  it  is  irritable  to  the  action  of  gravity. 
Since  gravity  is  exerted  always  in  the  same  direction,  it  is 
plain  that  reactions  to  this  force  cannot  be  studied,  as  in  the 
case  of  light,  by  altering  the  absolute  direction  in  which 
gravity  acts,  but  only  by  so  changing  the  position  of  the 
plant  that  the  force  acts  in  a  relatively  different  direction. 
The  reaction  to  this  stimulus  and  the  fixed  gravity  position 
must  not  be  confused  with  the  simple  effect  produced  by  the 
weight  of  the  parts  concerned.  Such  effects  are  to  be  seen 
in  the  downward  bending  of  some  plants  with  slender 
branches,  or  the  curvature  of  the  flower  or  fruit  stalks  by  the 
weight  of  the  parts.  True  geotropic  curvatures  are  brought 
about  by  acceleration  of  the  growth  of  the  irritable  cells, 
and  the  curvatures  produced  may  even  be  contrary  to  the 
direction  of  the  force.  If  seedlings  be  grown  in  boxes  upon 
the  rim  of  a  wheel  rotating  slowly  in  a  vertical  plane,  so  that 
they  are  successively  subjected  to  the  action  of  gravity  in 
relatively  different  directions,  it  will  be  seen  that  while  their 
members  grow  in  nearly  straight  lines,  the  direction  assumed 
by  the  stems  and  roots  is  quite  as  frequently  abnormal  as 
normal,  because  the  effect  of  gravity  which  normally  deter- 
mines the  direction  of  growth  of  these  axes  is  neutralized, 
since   it  now  acts  upon   them  from  a  new  direction  at  each 


190  PLANT    LIFE. 

successive   moment    (fig.    194).       If  the   wheel    upon  which 
such  seedlings  are  grown  be  rotated  at  a  high  speed,  the  cen- 


Fig.  194. — Seedling  mustard  plants  grown  on  a  cube  of  peat,  T,  attached  to  the  slowly 
rotating  axle,  A,  ./.  of  a  <linnst.it.     The  direction  of  growth  of  roots  and  steins  is 
controlled 
eliminated. 


:arness  of  moist  surfaces,  the  action  of  gravity  and  light  being 
ariable  direction  of  roots  and  stems.     At  m  and  /'/.j  aerial 


hyphaj  of  a  mold  have  taken  direction  as  far  from  the  repellant  moist  surfaces  as  pos- 
sible.    One  half  natural  size. — After  Sachs. 


trifugal  force  will  become  a  constant  one,  and,  acting  in 
place  of  the  neutralized  force  of  gravitation,  will  determine 
the  direction  which  the  stems  and  roots  will  assume.  Since 
the  primary  stems  of  most  plants  are  negatively  geotropic, 
when  grown  under  such  conditions  they  will  turn  toward  the 
center  of  the  wheel,  while  the  positively  geotropic  roots  grow 
toward  the  rim.  Similarly,  if  the  wheel  be  rotated  rapidly 
in  a  horizontal  plane  the  stem  will  be  controlled  by  a  com- 
bination of  the  force  of  gravity  and  the  centrifugal  force  (the 
latter  predominating  if  the  speed  is  great),  and  will  grow  in- 
ward and  upward,  while  the  roots  will  grow  downward  and 
outward  (fig.  195). 

288.   Transverse   geotropism. — Not    all   stems,   however, 
are  negatively  geotropic,  nor  all   roots  positively  geotropic. 


THE   MOVEMENTS    OF  PLANTS. 


I99 


The  central  axis  of  both  root  and  stem  in  the  majority  of 
plants  is  so,  but  lateral  branches  of  both  place  themselves  at 
an  angle  to  the  action  of  gravity,  sometimes  at  a  right  angle, 
at  other  times  at  a  highly  obtuse  or  acute  angle.  That  is, 
they  are  more  or  less  perfectly  transversely  geotropic.    What- 


Fig.  195. — Part  of  centrifuge,  a,  the  axle,  rotated  at  a  high  speed  by  water  or  electric 
motor,  to  which  is  attached  the  circular  metal  plate,  r,  r,  carrying  a  disk  of  cork,  A-. 
To  the  latter  are  attached  two  seedling  beans,  .(,  B,  by  means  of  pins;  rf,  the  primary 
stem;  k,  the  primary  root.  Over  the  seedlings  the  cover,  g,  is  placed  to  keep  them 
moist.  After  a  few  hours  the  lateral  roots  have  turned  into  the  direction  of  the  cen- 
trifugal force,  which  was  sufficiently  powerful  to  overcome  that  of  gravity  except  near 
axis  of  rotation,  .r.     One  half  natural  size. — After  Sachs. 


ever  the  normal  position  of  any  organ,  it  will  be  regained  by 
the  growing  parts  as  rapidly  as  possible  when  the  plant  is 
forcibly  displaced.  This  can  only  be  brought  about  by  the 
curvatures  produced  by  unequal  growth  of  the  younger  parts. 

If  a  potted  plant  be  laid  upon  its  side  for  a  short  time  and 
then  erected  before  any  response  to  the  stimulus  occurs  its 
growing  parts  still  curve  to  one  side,  although  not  so  far  as  if 
they  had  been  allowed  to  remain  in  the  horizontal  position. 

289.  Grasses. — In  only  a  few  cases  do  the  maturer  parts 
of  plants  regain  their  power  of  growth  under  the  stimulus  of 
gravity.  The  basal  portion  of  the  intcrnodes  of  grasses, 
however,  remain  for  a  long  time  capable  of  growth  ;   hence, 


200 


PI.AXT   LIFE. 


when  grasses  are  Mown  down  or  trampled  their  stems  erect 
themselves  by  the  geotropism  of  this  basal  growing  zone 
(fig.  196). 


Vu..  196. — Part  of  a  wheat-stalk,  showing  strong  geotropic  curvature.  The  shoot  was 
placed  horizontal,  and  the  growth  of  the  basal  part  of  the  internode  with  the  leaf-sheath 
connected  with  it  was  stimulated  on  the  under  side,  the  upper  remaining  short.  No 
curvature  occurs  in  the  older  part  of  the  internode.  About  two  thirds  natural  size. 
—After  Pfeffe:-. 


Fig 


io.  107.— Root-cage,  <  in  the  lower  edge  of  a  sheet  ol  zim  .1  little  larger  than  the  panes 
of  glass  selected  is  formed  a  water-tight  trough  oi  the  same  material.  Two  panes  of 
glass  of  suitable  size  are  clamped  together,  with  a  piece  of  wood  i  cm.  thick  on  three 
edges  to  keep  them  separate.  Seeds  are  sown  in  fine  soil  evenly  packed  between  the 
panes:  these  are  set  with  the  lower  edge  in  the  water-trough  and  a  sheet  of  zinc  is 
used  to  keep  out  light.  The  cage  should  be  slightly  inclined,  as  shown,  so  as  to  keep 
roots  against  the  glass      1  rom  1  drawing  by  J.  C.  Arthur. 


THE   MOVEMENTS    OF  PLANTS. 


20 1 


290.  Root-cage. — Experiments  upon  the  response  of  root- 
lets to  the  stimulus  of  gravity  upon  altering  their  position 
may  be  carried  on  by  means  of  a  root-cage,  shown  in  figure 
197.  It  consists  essentially  of  two  panes  of  glass  placed  close 
together,  between  which,  in  finely  sifted  soil,  the  rootlets  are 
grown.  By  inclining  this  root- 
cage  at  various  angles  it  may  be 
shown  that  not  only  the  primary 
root,  but  its  branches,  strive  to 
regain  their  normal  angle  with 
the  direction  of  gravity.  This 
is  illustrated  in  figure  198,  in 
which  the  dark  portion  of  the 
rootlets  represents  the  growing 
parts  while  the  cage  was  in- 
verted. They  then  took  about 
the  same  angle  with  the  horizon 
as  when  in  normal  position. 

Many    dorsiventral    organs, 


system  of  a  broad 
own  in  a  root-cage,  first   in  the 


in  the  normal  position.    The  arrow 


aga 

sshc 


Slich  as    leaves,   are    transversely      the  direction  in  which  gravity  acted 

the  different  positions.     The  black  por- 

geOtropiC,     JUSt      as     leaves     are      tion  of  the  roots  were  the  parts  growing 

.  during    inversion.      Two    thirds  natural 

transversely  hebotropic  size.— After  Sachs. 

291.  Twining  plants. — The  movements  of  twining  plants 
are  due  to  a  peculiar  reaction  to  gravity.  As  the  upper  inter- 
nodes  of  a  seedling  elongate  they  soon  become  too  weak  to 
support  themselves  and  bend  over,  becoming  nearly  horizon- 
tal. When  this  occurs  the  growth  of  the  right  or  left  flank 
of  the  stem  near  the  bend  is  accelerated  (whence  the  stem  is 
said  to  be  laterally  geotropic).  The  horizontal  part  is  thus 
swung  around,  twisting  the  stem  and  bringing  a  new  Hank 
under  the  influence  of  the  stimulus.  If  in  its  continued  rota- 
tion the  stem  comes  in  contact  with  a  nearly  ere<  t  support 
the  free  part  continues  to  rotate,  growing  longer  at  the  same 
time,  and  encircles  the  support.      The  part  below  the  point 


PLANT   LIFE. 


Fig.  199.- 


a    bit   of   the   stem  of  the  - 


of  contact  now  becomes  negatively  geotropic,  and  its  growth 
on  all  sides  is  equally  accel- 
erated. The  coils  are  thereby 
straightened  until  the  stem 
clasps  the  support  very  closely, 
from  which  it  is  often  prevented 
from  slipping  by  angles  or  out- 
growths of  various  kinds,  which 
roughen  the  surface  (fig.  199). 

While    gravity    thus    plays    a 
large  part    in    determining    the 

(-^?H\  'fffl'''ll^      position  of  both  aerial  and  sub- 

'^""i  Tpfoj^'f     terranean    organs,    it    must    be 

remembered  that  it  works  con- 
jointly with  many  other  stimuli, 
hop,  .'showing  the   six   angles,  each  The   position    of   the    members 

carrying  a  row  ot  emergences,  crowned  1 

by  a  branched  rigid  hair  with  very  sharp  jg     therefore,     a    resultant    of   the 

points.      Magnified   3   diam.      />,  three 

emergences  more    highly  magnified.-  reactions  to  the  various  external 

After  Kemer. 

forces  which  stimulate  it. 
292.  ((/)  Hydrotropism. — Hydrotropism  is  the  state  of  a 
plant  or  an  organ  when  it  is  irritable  to  moisture.  Hydro- 
tropic  organs  may  bend  toward  or  away  from  a  moist  surface. 
Roots  are  particularly  sensitive  to  the  presence  of  moisture. 
If  a  cylinder  of  wire  gauze  be  filled  with  damp  sawdust  and  a 
number  of  seeds  planted  near  its  surfa<  e  they  germinate  and 
the  roots  start  to  grow  in  the  normal  direction — i.  e.,  directly 
downward.  If  now  the  cylinder  be  suspended  at  an  angle, 
as  shown  in  figure  200,  the  roots  which  pass  into  the  air, 
stimulated  by  the  moisture,  curve  toward  the  damp  sawdust. 
Upon  entering  it  the  stimulus  ceases,  and  they  start  again  to 
grow  downward,  being  positively  geotropic.  Again  the 
Stimulus  of  the  moist  surface  overcomes  that  of  gravity,  and 
they  turn  back  to  it,  often  threading  themselves  in  and  out 


THE    MOVEMENTS   OF  PLANTS.  203 

of  the  wire  gauze.  Since  only  one-sided  action  of  a  stimulus 
determines  direction  of  movement,  if  the  air  be  saturated 
they  continue  to  react  to  the  stimulus  of  gravity  alone. 

293.  (t)  Movements  due  to  contact. — Contact,  either 
gentle  or  forcible,  and  friction  act  as  stimuli  to  modify  the 
growth  of  many  plant  parts.  Only  rarely  is  the  main  axis  of  a 
plant  sensitive  to  mechanical  stimuli,  except,  perhaps,  to  long 
J 


Fir,.  200. — Apparatus  for  demonstrating  hydrotropism.  <i.  a,  a  zinc  disk,  with  hooks 
to  which  is  attached  a  cylinder  or  trough  of  wire  netting  filled  with  damp  sawdust.  In 
this  are  planted  peas,  g;  whose  routs,  li,  i.  k,  m,  first  descend  into  the  air  but  soon  turn 
toward  the  damp  sawdust  again,  m  lias  threaded  itself  in  and  out  of  the  netting. — 
After  Sachs. 

continued  contact  (or  pressure)  in  the  case  of  some  twining 
plants.  But  in  many  plants  lateral  axes  in  the  form  of  ten- 
drils (*^\  115,  158)  and  leaf-stalks  (^j  157)  are  irritable  to 
contact,  even  to  a  degree  far  surpassing  that  of  our  nerves  of 
touch. 

If  the  tip  of  a  tendril  (•[  266),  while  still  capable  of  growth, 
come  in  contact  with  a  solid  body,  it  will  quickly  become 
concave  on  the  side  touched,  and  thus  will  wrap  about  the 
object,  if  it  be  of  suitable  size.  This  curvature  is  due  first  to 
the  shortening  of  the  cells  upon  the  concave  side  and  later 
to  unequal  growth    on    opposite   sides.      Finally  this   effect 


204  PLANT   LIFE. 

extends  to  all  parts  of  the  tendril,  which  begins  to  curve. 
As  both  ends  are  fast,  it  is  a  mechanical  necessity  that  the 
curves  become  spiral  coils,  both  right-  and  left-handed,  ac- 
companied by  a  twisting  of  the  tendril  on  its  axis  (  fig.  107). 
After  the  coils  are  formed  the  tissues  of  the  tendril  become 
thick-walled  and  rigid,  so  that  the  plant  is  attached  to  the 
support  by  a  series  of  spiral  springs. 

Other  tendrils  do  not  nutate,  but  are  negatively  heliotropic, 
and  by  contact  their  tips  are  stimulated  to  develop  disks 
which  apply  themselves  closely  to  the  support,  and  send  into 
its  irregularities  short  outgrowths  from  the  surface  cells. 
Such  plants  are  adapted  to  support  themselves  by  walls,  tree- 
trunks,  etc.  The  Japanese  ivy  and  one  form  of  the  Virginia 
creeper  are  notable  examples. 

The  coiling  of  the  leaf-stalks  is  not  unlike  the  first  curva- 
tures described  for  tendrils  (fig.  154). 

294.  (B)  Movements  of  turgor.— The  movements  just 
described  are  confined  to  members  which  are  growing  either 
throughout  or  in  some  part.  As  turgor  can  affect  only  tis- 
sues whose  cell-walls  are  elastic  (*j  188),  the  movements 
produced  directly  by  variation  in  turgor  can  occur  in  such 
mature  members  only  as  are  provided  with  special  motor 
organs.  In  almost  all  cases  these  are  leaves.  Stimuli  which 
regulate  growth  (^[  284)  may  also  affect  motor  organs,  pro- 
ducing like  curvatures.  But  elongation  of  any  part  of  a  motor 
organ  by  increased  turgor  is  reversible,  not  permanent,  (cf. 

II  254)- 

295.  Motor  organs. — The  motor  organ  in  leaves  is  usually 
the  leaf  base  (^[  151)  or  a  modified  portion  of  the  petiole, 
sometimes  greater  but  generally  less  in  diameter  than  the 
rest.  Its  cortex  consists  of  large,  rather  thick-walled,  pa- 
renchyma cells,  and  the  stele  occupies  a  relatively  small  part 
of  the  transverse  section.  In  other  parts  of  the  petiole  the 
stele  is  much  larger,  or  there  may  be  several  steles  distributed 


THE   MOVEMENTS    OE  PLANTS. 


205 


about  the  center.  (See  ^[  164.  ) 
show  the  contrast.  If  the  leaf 
be  a  compound  one,  there  are 
usually  secondary  motor  or- 
gans at  the  base  of  the  leaf- 
lets, as  in  the  leaf  of  the  bean 
(fig.  202).  Variation  in  the 
turgor  of  the  cells  of  the  cor- 
tex upon  one  side  or  the  other 
produces  a  sharp  curvature  of 


In    figure 


I  and  B 


Fig.  201.  Fig.  202. 

Fig.  201.  — Transverse  sections  through  petiole  of  scarlet  runner,  ./.through  the  rigid 
portion;  B,  through  the  motor  organ.  G,  g,  vascular  bundles;  ..  cortex;  w,  pith; 
r,  deep  channel  along  ventral  siiU-  oi  petiole.    Magnified  about  10  diam.— After  Sat  hs. 

Fig.  202. — Portion  ol  .1  scarlet  runner,  which,  originally  growing  erect,  has  been  inverted 
for  several  hours,  resulting  in  geotropic  curvatures  ol  the  primary  motoi  organs  /',  /"', 
ln.  The  lowest  pair  oi  leaves  show  secondary  motor  organs  at  the  juncture  of  petiole 
and  blade.  Similar  ones  are  present  in  the  upper  compound  leaves,  but  are  not  .  lcarly 
shown  in  the  figure.  The  arrows  show  the  position  oi  the  petioles  when  the  plant  was 
first  inverted.     About  two  thirds  natural  size —After  Sachs. 

the  motor  organ,  which  alters  the  position  of  the  leaf  or  leaflet 
(fig.  202).  The  concave  surface  of  the  motor  organ  is  always 
deeply  wrinkled  transversely,  while  the  convex  surface  is 
smooth. 


206  PLANT  LIFE. 

296.  Spontaneous  movements. — Only  a  few  plants  exhibit 
spontaneous  movements  through  the  motor  organs.  The  lat- 
eral leaflets  of  the  telegraph  plant  (s,  fig.  203),  under  normal 

conditions  of  rather  high  temperature  (at 
least  220  C),  show  jerky  movements  of 
such  direction  that  their  tips  describe  an 
irregular  ellipse,  which  is  completed  in 
1  to  3  minutes.  The  leaflets  of  the 
clovers  and  oxalis  show  much  slower 
movements  (of  a  few  hours  period), 
which  are  usually  obscured  by  the  light 
movements  described   in  the  next  para- 

Fig.  203. — Leaf  of  Hesmo-   ____t, 
diu.l     gyrans.      Two   graph. 

Sa,crhsnatural slze~After  More  commonly  the  turgor  movements 
are  induced.  The  most  common  stimuli  are  light  and  con- 
tact, although  many  others  suffice  to  induce  them. 

297.  Photeolic  movements. — Movements  produced  by  the 
withdrawal  of  light  have  long  been  known  as  "sleep  move- 
ments ;"  more  properly,  photeolic  movements — that  is,  move- 
ments induced  by  variation  of  light.  They  are  best  observed 
upon  the  leaves  of  the  bean  family,  though  many  other  plants 
exhibit  them.  Figure  204  shows  the  positions  assumed  by 
various  leaves  toward  nightfall.  It  will  be  seen  that  in 
compound  leaves  the  leaflets  sometimes  rise,  so  as  to  apply 
their  outer  faces  to  each  other ;  others  sink,  so  that  the  un- 
der surfaces  are  in  contact ;  others  become  folded  in  various 
ways.  This  position  is  maintained  throughout  the  night. 
Upon  the  increase  of  light  in  the  morning,  the  day  position 
is  assumed.  The  cutting  off  of  light  artificially  from  any  of 
these  plants  causes  them  within  a  short  time  to  assume  the 
nocturnal  position.  Darwin  suggested  that  the  nocturnal 
position  prevents  the  loss  of  heat  by  radiation  and  consequent 
injury  from  light  frosts.  But  it  is  not  by  any  means  certain 
that  this  is  its  real  purpose. 


THE   MOVEMENTS   OF  PLANTS. 


207 


298.  Contact  movements. — Some  organs  arc  sensitive  to 
contact,  as  the  leaves  of  Venus'  fly-trap  and  other  related 
plants.  The  motor  organ  in  the  Venus'  fly-trap  (figs.  386, 
205)  is  the  cushion  of  tissue  running  along  the  dorsal  side  of 
the  leaf  between  the  two  lobes.      By  the  sudden  variation  in 


Fig.  204. — Photeolic  movements,  a,  leaf  of  a  mimosa  in  day  position  ;  a',  the  same  in 
night  position.  />,  leaf  of  Coronilla  varia  in  day  position  ;  />',  the  same  in  nighl  po- 
sition, r,  leaf  of  A  mor&ka  fruticosa  in  day  position  ; <■'.  the  same  in  night  position. 
</,  leaf  of  Tetragonolobus  in  day  position  ;  </',  same  in  night  position, — Alter  Kemer. 


turgor  of  some  of  these  cells  the  two  halves  of  the  leaf  are 
thrown  quickly  together  when  one  of  the  six  bristles  upon  its 
upper  surface  is  touched.  The  sensitise  plant  drops  one  of 
its  leaflets  or  the  whole  leaf  quickly  when  stimulated  by  con- 
tact, heat,  or  electricity.     The  position  of  the  leaves  when 


208 


PLANT  LIFE. 


normally  expanded  is  shown  in  figure  206,  and  their  position 
after  stimulation  by  figure  207.  The  stamens  (^[  344)  of 
some  flowers  and  the  stigmas  (^j  336)  of  others  are  sensitive 


Fig.  206.  Fir,.  207. 

Fig.  205. — Part  of  a  transverse  section  of  a  leaf  of  Venus'  fly-trap,  in,  the  cushion  of 
tissm-  constituting  the  motor  organ ;  />,  one  of  the  sensitive  bristles  which,  upon  being 
touched,  cause  the  leaf  to  close ;  /,  one  of  the  interlocking  teeth.  The  minute  pro- 
jections over  inner  (ventral)  surface  are  glands  which  secrete  the  digestive  fluid  and 
later  absorb  the  food.     Magnified  about  5  diam. — After  Kurz. 

Fig.  206. — A  leaf  of  the  sensitive  plant  fully  expanded.     Natural  size. — After  Duchartre. 

In..  207. — A  leaf  of  the  sensitive  plant  after  stimulation.  The  motor  organ  at  the  base 
of  each  leaflet  has  thrown  it  forward  and  upward ;  the  motor  organs  at  the  base  of  the 
four  divisions  have  moved  them  together.  The  motor  organ  at  the  base  of  the  main 
petiole  has  moved  the  whole  leaf  sharply  downward.     Natural  size. — After  Duchartre. 

to  a  touch,  shortening,  elongating,  or  bending  in  such  a  way 
as  to  promote  pollination  (*|  358). 

The  motor  organs  of  the  leaves  of  a  number  of  the  bean 
and  oxalis  families  also  react  to  more  violent  mechanical 
stimuli.  Their  movements  are  similar  to  those  described  in 
U  297- 


PART  III:   REPRODUCTION. 


CHAPTER    XVI. 

INTRODUCTION. 

Having  considered  in  Parts  I  and  II  the  structures  and 
functions  by  which  the  nutrition  of  the  individual  is  secured, 
Part  III  is  devoted  to  the  consideration  of  the  structure  and 
functions  of  the  reproductive  organs  and  the  functions  by 
which  a  succession  of  similar  individuals  is  insured. 

One  of  the  fundamental  powers  of  protoplasm  is  its  ability 
to  produce  new  organisms  as  offspring  from  the  older  ones. 
In  the  simpler  plants  the  two  great  functions,  nutrition  and 
reproduction,  are  often  carried  on  by  the  same  cell.  This 
must  always  be  so  in  the  unicellular  plants.  In  the  higher 
plants,  however,  these  two  functions  become  completely  sep- 
arated, organs  being  specialized  for  each,  so  that  the  func- 
tions may  be  more  certainly  and  efficiently  performed. 

299.  Reproductive  structures. — Any  part  capable  of  grow- 
ing into  a  new  individual  may  be  called  a  reproductive  body,  and 
the  part  on  which  or  in  which  it  is  produ*  ed  is  a  reproductive 
organ.  If  the  reproductive  bodies  consist  of  one  or  two  cells 
only,  they  are  usually  called  spores,  [f  they  are  cell-aggre- 
gates, they  are  generally  called  brood  buds  or  gemmcei  to  dis- 
tinguish them  from  ordinary  buds.  In  both  cases  it  is  neces- 
sary that  the  cells  to  be  separated  from  the  parent  should  be 
capable  of  growth — that  is,  in  the  condition  known  as  the 
embryonic  phase  (•[  256).     The  reproductive  organs  pro- 

209 


2IO  PLANT   LIFE. 

duced  by  some  plants  are  exceedingly  complex  and  varied, 
while  others  form  reproductive  1  todies  in  very  direct  ways. 
The  reproductive  bodies  themselves  are  generally  very  simple. 
In  addition  to  complex  reproductive  organs,  there  are  some- 
times accessory  parts  by  which  the  plant  adapts  its  reproduc- 
tive functions  to  the  conditions  under  which  it  lives.  Among 
these  accessory  structures  are  many,  as  among  the  flowers  of 
seed  plants,  by  which  the  aid  of  other  plants  or  animals  is 
secured. 

300.  Vegetative  and  sexual  reproduction. — In  all  the 
diversity  of  organs  and  processes  two  chief  methods  may  be 
distinguished,  called  vegetative  reproduction  and  sexual  repro- 
duction . 

Vegetative  reproduction  consists  in  the  formation  of  repro- 
ductive bodies  by  processes  of  growth  only.  The  modes  in 
which  they  arise  are  varied  in  detail,  but  consist  essentially 
in  the  production  by  the  parent  of  a  body,  unicellular  or 
multicellular,  which  at  maturity  develops,  under  suitable 
conditions,  into  a  new  plant. 

Sexual  reproduction  consists  in  the  formation  of  reproduc- 
tive bodies  by  the  union  of  two  specialized  cells,  neither  of 
which  alone  is  capable  of  developing  into  a  new  plant. 


CHAPTER    XVII. 
VEGETATIVE   REPRODUCTION. 

I.  Fission  and  budding. 

301.  Fission. — In  single-celled  plants  cell  division  and 
reproduction  are  practically  identical,  since  shortly  after  divi- 
sion occurs  the  two  cells  so  produced  separate  and  lead  an 
independent  existence  (C,  fig.  18).  Such  a  method  of  repro- 
duction evidently  interferes  little  with  the  processes  of  nutri- 
tion, which  probably  are  scarcely  even  suspended  during  the 
process  of  reproduction. 

302.  Budding. — A  slight  variation  of  the  method  of  fission 
just  described  is  to  be  found  in  those  single-celled  plants, 
such  as  the  yeasts,  whose  growth  is  so  localized  as  to  form 
upon  one  side  a  small  enlargement  which  ultimately  attains 
the  size  of  the  parent,  with  which  it  is  connected  by  a  very 
narrow  neck  (fig.  48).  Across  this  neck  the  partition  wall  is 
formed  in  the  usual  way.  This  becomes  mucilaginous,  ren- 
dering the  adhesion  of  the  daughter  cell  at  this  point  so  weak 
that  it  is  easily  separated  from  the  parent.  This  method  of 
reproduction  is  known  as  budding. 

303.  Fragmentation. — In  those  plants  which  consist  of 
a  row  of  cells  more  or  less  closely  united,  the  breaking  up  of 
the  filaments  into  separate  pieces,  either  through  externa] 
force  or  the  death  of  one  of  the  cells,  may  produce  a  number 
of  smaller  colonies  or  of  new  individuals,  each  of  which  may 
grow  to  full  size.  In  some  of  the  more  looselv  organized 
filament-colonies,  such  as  Nostoc  (see  •  13,  and  figs.  1  }, 
14),  there  are  specialized  cells  whose  function  seems  to  be 

21 1 


212  PLANT   LIFE. 

to  loosen  pieces  of  definite  length,  which  creep  out  of  the 
jelly,  grow,  and  thus  produce  new  colonies. 

The  greater  size  reached  by  most  multicellular  plants  soon 
renders  impossible  the  continuance  of  this  method  of  repro- 
duction, except  among  those  whose  cells  arc  all  alike.  Should 
such  separation  into  nearly  equal  parts  occur  among  more 
highly  specialized  plants,  it  is  evident  that  one  portion  might 
easily  be  left  without  nutritive  organs  adapted  to  its  needs. 
The  higher  plants,  therefore,  specialize  certain  regions  or 
members,  where,  by  division  or  budding  or  similar  processes, 
reproductive  bodies  may  be  formed. 


II.  Spores. 

304.  Sexual  and  non-sexual  spores. — A  spore  is  a  single- 
celled  body  capable  of  producing  a  new  plant.  Spores  may 
be  formed  either  by  a  process  of  growth  or  by  a  sexual  act — 
i.e.,  the  union  of  two  cells.  The  former  are  called  non- 
sexual spores  ;  the  latter,  sexual  spores.  Only  non-sexual 
spores  are  discussed  in  this  chapter. 

305.  Structure. — While  a  spore  is  generally  composed  of 
one  cell,  the  term  is  extended  to  include  two-  to  many-celled 
bodies  which  are  formed  in  the  same  way  as  the  simpler 
ones.  In  fact,  no  clear  distinction  in  form  or  structure  can 
be  drawn  between  spores  and  brood-buds.      (See  1"  361.) 

306.  Motile  spores. — Spores  may  be  either  naked  and 
motile  or  furnished  with  a  cell-membrane  and  non-motile. 
The  former  are  commonly  produced  by  plants  which  pass  all 
or  part  of  their  lives  in  water,  such  as  the  algre  and  aquatic 
fungi.  They  are  usually  pear-shaped  and  furnished  with  one 
or  more  cilia,  by  means  of  which  they  swim  about  (fig.  168). 
When  locomotion  was  supposed  to  be  a  distinctive  power  of 
animal  bodies  they  were  called  zoospores,  a  name  still  re- 
tained.     They  are  also  called  swarm-spores. 


VEGE  TA  Tl  I  E  REPROD  UCTION. 


213 


When  zoospores  possess  chlorop 
quently  do,  they  are  aggregated  at 
the  larger  end,  leaving  the  pointed 
end  to  which  the  cilia  are  attached 
colorless.  Zoospores  are  formed 
either  in  a  general  body-cell,  not 
visibly  different  from  the  other 
body-cells,  or  in  a  cell  specialized 
in  form  and  structure.  In  either 
case  the  cell  in  which  they  are  pro- 
duced is  called  a  zoosporangium. 
The  entire  contents  of  the  zoospo- 
rangium may  form  a  single  zoospore, 
or  it  may  divide  into  several  or 
many.  In  the  latter  case  the  nu- 
cleus divides  into  two  or  more,  each 
of  which  gathers  about  itself  a  por- 
tion of  the  protoplasm.  The  zoo- 
spores are  set  free  by  the  rupture  of 
the  wall  of  the  sporangium  or  by 
the  solution  of  a  portion  of  the  wall 
(fig.  208).  They  may  begin  to 
move  before  the  rupture  of  the  wall, 
in  accomplishing  which  their  activ- 
ity may  materially  assist.  They 
then  work  their  way  out  and  swim 
freely  in  the  water.  After  a  time 
of  movement  they  usually  lose  their 
cilia,  either  withdrawing  them  into 
the  protoplasm  or  dropping  them 
off,  come  to  rest,  and  begin  to  grow 
into  a  new  plant. 

307.  Non -motile  spores  are 
formed  by  all  classes  of  Land  plants 


l'n.    208    -Development  and  escape 

of  zoospores  of  an  aquatic  fungus 
{Saprolegnia  lactea).    The  ends 

ot   two  hvph.e  are  shown,  the  ter 

minal    cells    being    goosporangia 

In  ,;.  the  protoplasm  1 

ing  about  the  numerous  nui  lei  (no 

shown).  From  6  many  ol  tin-  ZO 
ospores  have  escaped  through  the 
perforation   in    the  wall   near  the 

upper  end  of  tin-  .ell.      From       ."11 

have  est  aped  hut  one.  whk  h  is  just 

slipping  through  the  opening  (  here 

in  profile).    Magnified  300  diam. — 

Aftei    kerner. 

without  exception.    They 


^■4  PLANT   LIFE. 

are  often  produced  in  great  profusion,  especially  by  the  fungi, 
the  mosses,  the  ferns,  and  the  seed  plants. 

308.  Form  and  structure. — Their  form  is  exceedingly 
various.  Many  are  spherical  or  ovoid,  while  some  are  cylin- 
drical or  even  needle-shaped  (figs.  213,  228,  271).  Irregular 
forms,  also,  are  not  uncommon. 

In  structure  spores  are  usually  only  single  cells,  specialized. 
Each  is  a  nucleated  mass  of  protoplasm  surrounded  by 
a  cell-wall  which  may  be  either  thin  or  thick,  according 
as  the  spore  is  destined  to  immediate  growth,  or,  as  a 
resting  spore,  to  endure  for  a  time  unfavorable  conditions. 
In  some  cases  the  wall  of  even  the 
'  ')  JL[\A -'Jf/fr  thin-walled  spores  has  two  layers,  a 
condition  which  is  almost  universal 
among  resting  spores.  When  the 
wall  is  so  differentiated  the  inner 
layer  is  delicate,  rarely  thickened, 
extensible,  and  composed  of  more  or 
less  unaltered  cellulose.  The  outer 
layer  is  often  irregularly  thickened, 
so  that    its  surface   is  covered   with 

Fig.    2oo.-Section    of    a    mature  ria^es,     WartS,     Spines,      Or     boSSCS     of 

rt"el^of^fdf(co&  various  sorts   (figs.    210,   248,    271, 
u;r!-rVu;ettcZ,.^'u1e'399)-      "    is   brittle,    as   compared 
S^pma^tT^ndiwith   the  inner  coat,   and  is  usually 
^VedaTo«tatisoStdiaSre-fe-more  or  less  altered  in  composition 
from    its     original    cellulose   nature. 
A    third    layer  (the  epispore)   is   sometimes  present,  but  this 
is  not  produced  by  the  cell  which  it  surrounds.      It  is  added 
from   the   outside,    being   derived    from  the   protoplasm   sur- 
rounding the  spores  after  they  are  formed*   (fig.  209).    This 
form  of  spore  is  common  among  the  fern  allies. 

*  This  protoplasm  often  comes  from  the  disorganization  of  some  of  the 
tells  around  the  chamber  in  which  the  spores  lie. 


VEGETATIVE   REPRODUCTION. 


215 


309.  Food. — In  almost  all  cases  there  is  a  supply  of  reserve 
food  within  the  spore.  This  reserve  food  varies  in  amount 
with  the  conditions  under  which  the  spores  are  formed.  It 
is  ordinarily  greater  in  resting  spores  than  in  those  intended 
for  immediate  growth.  Spores  may  contain  chlorophyll,  but 
generally  do  not ;  even  the  spores  of  green  plants  are  mostly 
without  it.  Its  presence  seems  to  indicate  an  active  condition 
of  the  protoplasm,  and  the  vitality  of  such  spores  is  usually 
of  short  duration.  It  is  of  course  absent  from  the  spores  of 
colorless  plants,  such  as  the  fungi. 


Fig.  210. — Part  of  a  vertical  section  of  a  leaf  of  a  willow,  attacked  by  a  fungus  (.!/<•/<!»//- 
sora  salicimi).  eo,  epidermis  of  upper  side  lifted  by  the  young  teleuto  spores;  /,  de- 
veloping from  the  spore-bed  above  the  ends  of  the  palisade  parenchyma,  />nr ;  en, 
epidermis  of  the  under  side,  broken  through  spore-bed  from  which  spring  uredo- 
spores,  st.  and  paraphyses,  /•.  eo  will  also  finally  be  ruptured  to  set  free  /.  Magni- 
fied 260  diam. — After  Prantl. 

310.  Growth. — Spores  germinate  by  absorbing  water,  thus' 
bursting  the  more  rigid  layer  or  layers  of  the  cell-wall.  The 
inner  layer  then  grows  in  area  to  accommodate  the  increas- 
ing protoplasm,  which  so  controls  the  regions  of  growth  and 
the  mode  of  cell  division  as  to  produce  a  plant  of  definite 


216 


PLANT  LIFE. 


form.  In  many  cases  the  plant  produced  is  essentially  like 
that  which  gave  rise  to  the  spore.  In  others  it  is  different, 
but  sooner  or  later  in  the  life  cycle  the  same  form  recurs. 
Variety  of  bodily  form  is  common  among  the  fungi,  in  which 
it  is  called  pleomorphism.  Among  plants  showing  well-de- 
fined alternation  of  generations  (r€;  55,  320),  the  non- 
sexual spores  are  produced  by  one  form  only,  and  always 
give  rise  to  the  other. 

311.  Origin. — Non-motile  spores  are  either  free,  being 
produced  at  the  ends  of  branches  specialized  for  that  purpose, 
or  enclosed  in  a  case  called  a  sporangium.  Often  the  same 
plant  forms  spores  by  both  methods  at  different  stages  in  its 
development. 


Fig.  211. — Diagrams  showing  the  formation  of  an  acropetal   sin.iicli.iiii  by  budding. 
a,  the  spore-producing  hypha  :  b,  its  terminal  c  < •  1 1  showing  a  bud  which  in  c  has  ma- 

tured   into  .1  spore  ;   (t,  the  spore  <    has  budded,  anil  so  on,  until  in  h   five  spores  have 
been  formed,  numbered  in  order  of  their  development.-  Alter  Zopf. 

312.  Free  spores. — The  formation  of  free  spores  is  con 
fined  to  the  lower  plants,  and  is  especially  characteristic  of 
the  non-aquatic  fungi.  The  branches  producing  spores  may 
occur  singly,  or,  more  commonly,  they  are  aggregated  at 
certain  points,  forming  a  spore-bed  (fig.  210).  If  the  fungus 
develops  its  mycelium  in  the  interior  of  a  host,  the  formation 
of  a  spore-bed  is  often  necessary  to  rupture  the  host,  so  that 


V  EG  ETA  TIVE   REP  ROD  UCTION. 


217 


the  spores  may  be  brought  to  the  surface  and  set  free.  Thus 
the  spore-beds  of  parasitic  fungi  commonly  blister  the  surface 
of  the  host  by  lifting  up  its  outer  tissues  (eo,  fig.  210). 

313.  Spore-chains. — Spores  maybe  produced  either  singly 
at  the  ends  of  the  branches  or  in  chains.  When  produced  in 
chains,  the  youngest  spore  may  be  at  the  base  or  at  the  apex 
of  the  chain.  The  first  method  is  much  more  common  than 
the  second.  In  the  second  case  each  spore  must  arise  as  a 
bud  upon  an  older  spore,  budding  itself  to  form  a  younger  one 
(fig.  211).  The  spores  in  such  a  chain  are  limited  in  number. 
They  develop  rapidly,  and  all  are  loosened  at  about  the  same 
time.     Those  chains  which  have  the  oldest  spore  at  the  apex 


Fig.  212.— An  outline  showing  the  formation  oi  a  basipetal  spore-chain  of  the  blue-green 
mold  i Penicillium  glaucum),  6,  branch  oi  spou-  hearing  hvpha.  budding  beneath 
two  older  spores.  Across  the  narrow  net  k  a  partition  wall  is  formed,  the  spores  round 
off,  and  from  this  wall  a  device,  ..  for  loosening  the  spores  is  developed.  The 
terminal  spore  is  oldest.     Highly  magnified.-    Alter  Frank. 

Fig.  213.— Longitudinal  section  through  the  edge  oi  a  gill  of  a  mushroom  (Cofrinus) 
after  spore-formation  is  completed.  /,  interwoven  hyphae  ol  the  gill,  branching  to 
form  the  hymenium,  composed  ol  the  paraphyses,  /,  the  cystidia.  <  .  anil  the  ba- 
sidia,  /'.     The  latter  give  rise  to  tour  slender  I  nam  lies,  ulmsc  tips  enl.uge  1"  lorm  each 

a  single  spore,   /and.  do  not  produce  spores.    Magnified  300  diam.-  Alter  Brefeld. 

arc  produced  by  the  continued  division   of  the  branch  by 

transverse    partitions,    usually    preceded    by   budding    of  the 
apex,  often  described  as  constriction  (/>,  fig.  212).      Beneath 


2l8 


PLANT  LIFE. 


the  first  spore  so  formed  another  spore  is  produced  as  the  first 
grows  older  ;  and  this  process  continues  as  long  as  the 
plant  is  able  to  furnish  material  for  the  making  of  spores. 
In  such  cases,  often  the  oldest  spores  are  liberated  while 
new  ones  are  being  produced  at  the  base  of  the  chain. 

A  modification  of  the  production  of  spores  singly  occurs 
when  the  branch  destined  to  produce  them  gives  rise  to 
two  to  eight  very  slender  branches,  each  of  which  enlarges 
at  the  tip  into  a  single  spore,  so  that  the  main  branch  appears 
to  carry  two  to  eight  spores  upon  slender  stalks.  Such  a 
spore-producing  branch  is  called  a  basidium  (fig.  213).  It  is 
the  characteristic  form  in  the  higher  fungi,  which  produce 
conspicuous  fructifications. 


Fig,  214. — A,  a  puffball  (Octaviana)  halved,  showing  the  internal  chambers  (shaded 

dark)  lined  by  hymenium  (the  narrow  white  border).  The  intervening  spaces,  g, 
and  the  unshaded  outer  part  are  formed  of  interwoven  hvph.i  .  Magnified  5  diuin. 
/>',  a  bird's-nest  fungus  (Crucibulum)  halved.  The  similar  internal  chambers  have- 
been  loosened  by  the  disappearance  of  the  intervening  hyph.e  immediately  about  the 
hymenium  (represented  by  radiating  lines)  and  a  wavy  Stalk  by  which  each  remains 
loosely  attached.     Magnified  4  diam. — After  Luerssen. 


314.  Fructifications. — In  the  higher  fungi  whose  myce- 
lium is  developed  within  a  dead  substratum  many  brant  lies 
are  aggregated  to  constitute  a  reproductive  structure  or  fructi- 
fication, which  is  the  only  conspicuous  part  of  the  fungus. 
(For  an  account  of  the  vegetative  parts,  see  ^]^[  50,  54.) 


VEGE  TA  TI J 'E   RETROD  UCT10N. 


219 


The  body  of  the  fructification  is  made  up  of  hyphae,  more 
or  less  interlaced  and  adherent,  and  is  of  a  form  adapted,  not 
only  to  break  through  the  substratum,  but  also  to  furnish  an 
extensive  surface  for  the  spore-beds,  called  in  these  plants  the 
hymenium  (fig.  213).    The  hymenium  consists  of  the  enlarged 


Fig.  215. 
Fig.  215. — A  fructification   of   Clavaria 
a  i<  >  t\i.      The     hymenium    covers    the 
upper    part    of    the    branches.       Natural 
size.— After  Kerner.  FlG.  216. 

Fig.  216. — A  fructification  of  a  mushroom,  Amanita  phalloides.  /.  the  cap  or  pileus  ; 
?■,  the  veil,  originally  connected  with  edge  of  cap,  covering  the  gills  which  radiate  tnun 
the  stipe,  st,  to  the  edge  of  cap;  vo,  the  volva.  The  surface  ot  the  gills  is  covered 
with  the  hymenium.  Most  mushrooms  showing  a  distinct  volva  are  poisonous. 
Natural  size. — After  Kerner. 

free  ends  of  the  hyphae,  which  are  set  at  right  angles  to  the 
surface.  Some,  the  basidia,  develop  2-S  slender  branches 
each  of  which  produces  at  the  tip  a  single  spore.  The  hyme- 
nium may  be  formed  upon  the  outer  surface  of  the  fructifica- 
tion or  in  internal   chambers  (fig.   214).      In   the   latter  case 


220 


PLANT  LIFE. 


these  chambers  rupture  at  the  maturity  of  the  spores,  or  even 
earlier. 

The  fructification    may  be   irregularly    lobed,    sessile  and 
gelatinous,    or   much   branched  and  cylindrical  or  flattened, 


Fig.  217. — Fructification  of  Hydnum  imbricatum. 
The  surface  of  the  projecting  spines  on  the  under 
side  of  the  cap  are  covered  with  the  hymenium. 
Natural  size. — After  Kemer. 


with  the  hymenium  covering  the 
whole  or  the  upper  part  of  the  body, 
as  in  Clavaria  (fig.  215)5  or  it  may 
form  an  umbrella-like,  stalked  cap, 
as  In  toadstools,  with  the  hymenium 
extending  over  radiating  plates  on 
the  under  side  of  the  cap,  as  in  -  \gari- 
cus  (fig.  216),  or  over  spine-like  pro- 
jections in  the  same  region,  as  in 
Hydnum  (fig.  217);  or  it  maybe 
a  semicircular,  sessile  body  projecting 
from  the  substratum  like  a  shelf  or 
bracket,    with    the    hymenium    lining 


w  &i 


Fig.  218.— Trunk  of  an  ash  tree, 
showing  fructifications  of  Poly- 
porus  ig  na  rius.  Alter  a  pho- 
tograph by  Von  Tubeuf. 

innumerable    minute 


VEGETATIVE   REPRODUCTION.  221 

tubes  on  the  under  face,  as  in  Polyporus  (fig.  218) ;  or  it  may 
take  the  form  of  a  ball,  the  hymenium  arising  as  a  lining 
upon  the  walls  of  regular  or  irregular  internal  chambers, 
which  may  occupy  most  of  the  interior,  as  in  puffballs  and 
their  kin  (figs.  214,  219). 

315.   Sporangia. — Spores  are  also  formed  in  the  interior 
of  cells  which  are  either  free  or  covered  by  a  jacket  of  other 


Ik  Hs 


KW 


1^ 


Fig.  2ig. — Fructification  of  a  puffball  (Geaster  hygrometricus)  \  A ,  young  ;  />',  mature, 
the  outer  layer  split  open  and  recurved,  the  inner  also  broken  to  allow  escape  of 
spores.     Natural  size. — After  Corda. 


cells.  The  entire  structure  is  called  a  sporangium.  In  the 
first  case  the  sporangium  is  said  to  be  simple.  Its  wall  is  the 
wall  of  the  mother  cell  in  which  the  spores  are  produced, 
and  they  are  set  free  by  its  rupture  (fig.  220).  In  the  second 
case  the  sporangium  is  said  to  be  compound.  The  mother 
cells  of  the  spores  (rarely  only  one  mother  cell)  are  sur- 
rounded by  others  forming  a  jacket  of  greater  or  le>s  thick- 
ness. In  the  mother  cells,  which  are  differentiated  from  the 
investing  cells,  the  spores  are  formed  as  in  simple  sporangia. 
As  the  spores  mature  the  walls  of  the  mother  cells  burst  or 
are  disorganized,  leaving  the  spores  still  surrounded  by  the 
layer  or  lasers  of  investing  cells  (fig.  221).  This  jacket  is 
ruptured  sooner  or  later  and  the  spores,  thus  set  free,  are 
distributed  in  various  ways.      (See  %  475.) 


222  PLANT  LIFE. 

316.   Simple    sporangia. — The    simple   sporangium    may 
be  like  the  general  body-cells,  or  it  may  be  specialized  in 


Fig.  220. — Longitudinal  section  of  the  simple  sporangium  of  a  mold  (Mttcor).  The 
aerial  hypha,  //,  has  partitioned  off  a  cell,  .r,  within  which  spores  are  produced.  The 
walls  of  this  sporangium  are  studded  with  needle  crystals  of  calcium  oxalate.  The  par- 
tition protrudes  far  into  the  end  cell.     Magnified  260  diam. — After  Kerner. 

Fig.  221. — Longitudinal  section  of  the  stem,  s,  of  a  moss  gametophyte,  bearing  leaves, 
b.  Embedded  in  the  stem  is  the  sporophyte,  consisting  of  a  stalk,  st ,  and  a  compound 
sporangium,  of  which  w  is  the  wall,  formed  of  a  sheet  of  cells,  enclosing  the  spores, 
sp  (contents  not  shown).     Magnified  100  diam. — After  Hofmeister. 


form  as  well  as  in  function.  It  may  be  spherical,  sac-like, 
or  linear.  The  elongated  sporangium  produced  by  the  en- 
largement of  the  end  of  a  hypha  in  certain  fungi  has  received 
a  special  name,  ascus.  The  number  of  spores  formed  within 
a  simple  sporangium  may  be  two  or  more,  up  to  several 
hundred.  The  spores  are  formed  like  the  zoospores  de- 
scribed in  ^[  306,  with  the  difference  that  a  wall  is  secreted 
by  each  spore  be/ore  it  escapes. 

The  rupture  of  the  tell  wall,  which  sets  the  spores  free, 
is  brought  about  by  the  increase  of  the  spores  in  size,  or  by 
the  swelling  of  the  surplus  protoplasm  left  after  their  forma- 
tion. Preparatory  to  bursting,  the  wall  is  frequently  altered 
so  as  to  be  mucilaginous,  or  it  becomes  brittle.  In  some 
cases  a  certain  area  is  thin,  which  furnishes  a  starting-point 
for  the  rupture. 


V EG  ETA  TIVE    REPRODUCTION. 


223 


317.  Arrangement. — Simple  sporangia  may  occur  singly 
or  they  maybe  aggregated.  When 
aggregated,  they  usually  stand  side 
by  side,  and  constitute  a  layer, 
called  the  hymenium  (figs.  222, 
226).  (Compare  If  314.)  When 
thus  aggregated  (and  even  when 
single)  they  may  be  enclosed  by 
a  jacket  formed  by  the  coalescence 
of  sterile  filaments,  as  in  the  mil- 
dews, in  which  the  whole  structure 
constitutes  a  fructification  (figs. 
223,  224,  337).  In  the  lichens  the 
hymenium,  during  its  earlier  stages, 
is  partially  enveloped  by  sterile 
filaments  forming  a  cup-like  apo- 
thecium  (figs.  225,  226).  In  the 
cup  fungi  (fig.  222)  the  fructifica- 
tion, which  is  the  only  part  of  the 
fungus  above  the  substratum,  is  a 
single  apothecium,  whose  whole 
inner  face  is  the  hymenium.  In 
an  allied  form,  the  morels  (fig. 
227),  the  fructification  is  differ- 
entiated into  a  stalk  carrying  an 
enlarged  head  marked  by  narrow 
ridges  separating  broad  shallow  pits 
over  the  surface  of  these  depressed  areas.  In  other  fungi, 
the  sporangia  are  sunk  in  deep,  narrow-mouthed  pits  with 
which  the  outer  part  of  the  fructification  is  filled  (  fig.   22S). 

The  simple  sporangia  of  some  of  the  red  seaweeds  show  a 
transition  to  the  compound  type  in  being  formed  by  an  in- 
ternal cell  of  the  thallus  (fig.  229).  The  adjacent  cells,  how- 
ever,   do   not   constitute   a   special  wall,  nor  are   they    neces- 


[G.  222.  —  A  cup  fungus  {Peziza 
aurantid).  A,  three  fructifica- 
tions, about  natural  size.  The 
inner  surface  of  the  cup  is  covered 
with  a  hymenium,  a  bit  ol  which 
is  shown'  at  />'  in  section  at  right 
angles  to  surface.  /•,  paraphyses  ; 
,;.  an  asms  bursting  to  allow 
escape  of  spores.  Highly  magni- 
fied—After Keriler. 

The  hymenium  extends 


224 


PLANT    LIFE. 


sarily  ruptured  to  permit  the  escape  of  the  spores,  being 
often  displaced  in  the  development  of  the  sporangium,  so 
that  at  maturity  it  is  partially  free. 


Fig.  223. — A  mildew  (Erysipke  communis),  showing  the  mycelium  ramifying  over  a 
bit  of  leaf,  with  erect  spore-bearing  branches  and  globular  fructifications,  containing 
asci.     Magnified  about  175  diam.— After  Tulasne. 


318.   Compound  sporangia. — Simple  sporangia  occur  only 
among  the   lower   plants.      In   the   higher    plants,   including 
the  mossworts,   fernworts,  and  seed 
plants,    the     sporangium     is     always 
compound. 

319.  Development.  —  ( Compound 

sporangia  may  be  developed  either 

from     superficial    or    from     internal 

..  fr!,m  cells.      As  a  consequence,  the  mature 

the  interior  of  the  fructification  ■ 

rxa\&vn<ErysipkeHeraciei\  sporangia  will  be  either  free  or  more 

similar  to  those  shown  in  fig.  223.    '  n 

Each  as,  us  contains  four  spores.  or  less  enclosed  within    the  tissues  of 

Magnified  200  diam. — After  De- 

Bary.  the  organ  by  which  they  are  borne. 

A  superficial   cell    may    enlarge   so   as   to  protrude  from    the 

surface,  and  divide  into  two  parts,  of  which  the  upper  cell 

develops   into  the  sporangium  proper,  and  the  lower  cell   into 

its    stalk.      According  to    this   method    of   development    the 

sporangium  is  a  surface  appendage,  and  may  be  looked  upon 


VEGE  TA  77 1  E   RETROD  UCTION. 


225 


as    homologous    with   a    hair.        Sometimes    the  sporangia, 
although  really  free,  are  overgrown  by  adjacent  parts,  so  that 


Kig.  225.— A  lichen  {Parmelia  conspersa)  growing  on  a  stone,  showing  the  leaf-like 
thallus  (.mycelium1,  with  many  fructifications  lapothecia1.  The  older  ones  are  more 
or  less  irregular  and  large  with  a  narrow  rim  ;  the  younger  are  nearer  the  margin,  cir- 
cular, and  nearly  closed  over  at  top.     Natural  size. — After  Frank. 


Fig.  226.— A  vertical  section  of  an  apothet  ium  ol  a  li(  hen  1 ,  \  naptychia  ciliaris).  h, 
the  hymenium;  y,  the  subhymeruum,  a  layer. .1  densely  interwoven  hyphae;  .-.  r,  the 
sterile'  hyphae  which  partially  enclose  the  hymenium  ;  rn,  the  loosely  woven  hyphae  <>t 
the  thallus;  a,  the  algae  enslaved  by  the  fungus,    Magnified  about  50  diam.— After 

Sachs. 

they  are  enclosed  in  a  chamber,   whence  the  spores  est  apt- 
after  they  are  set  free  by  the  bursting  of  the  sporangium. 


226 


PLANT  LIFE. 


The  other  mode  of  development  produces  enclosed  spo- 
rangia. One  or  more  internal  cells  differentiate  and  become 
the  mother  cells  of  the  spores.     The  spores,  when  mature, 


Fig.  228. 


Fir..  227. — A  fructification  of  the  morel  (Morchella  esculentd).  The  hymenium  occu- 
pies the  surface  of  the  depressed  areas.     Natural  size. — After  Kerner. 

FlG.  228.— A  small  bit  of  a  section  through  the  fructification  of  the  ergot  (Claviceps 
purpurea),  showingone  ol  the  deep,  narrow-mouthed  pits,  P  (and  part  of  another), 
enclosing  the  asci.  From  the  broken  ascus  at  the  right  thread-like  spores  are  escap- 
ing.    Highly  magnified. 


-Alter  Tulasne. 


will  therefore  be  enclosed  by  the  adjacent  cells  of  the  plant, 
which  may  became  altered  so  as  to  form  a  sort  of  special  wall 
more  or  less  different  from  the  tissue  which  lies  farther  off. 


VEGE  TA  TIVE   REPROD  UCTION. 


227 


320.  The  sporophyte. — Among  the  mossworts,  fernworts, 
and  seed  plants  reproduction  by  non-sexual  spores  has  be- 
come so  fixed  and  important  that 
one  stage  in  the  plant  is  devoted 
especially  to  producing  them. 
This  phase  is  different  from  that 
producing  sexual  cells,  the  differ- 
ence becoming  greater  the  more 
complex  the  plant.  The  stage  set 
apart  for  spore  production  is  called 
the  sporophyte.  In  the  moss- 
worts  the  sporophyte  has  very 
little  green  tissue,  and  therefore 
carries  on  little  nutritive  work, 
but  depends  for  its  supply  of  food 
chiefly  upon  the  sexual  stage,  with 
which  it  is  connected  throughout 
its  entire  existence  (^|  68).  In 
the  fernworts  and  seed  plants, 
however,  the  sporophyte  possesses 
extensive  nutritive  tissues,  the 
leaves,  stems,  and  roots  belonging 
entirely  to  this  stage.  Sporangia 
in  these  plants  may  be  formed 
either  upon  the  stem  or  the  leaves 
— never  upon  the  roots. 

321.  Liverworts.  —  In  the 
liverworts  the  sporangium  is  gen- 
erally produced  at  the  upper  end 
of  a  short  or  long  stalk.  It  is 
either  spherical,  ovoid,  or  short- 
cylindrical  (figs.  64,  65).  The 
spore-producing  tissue  occupies  the  greater  part  of  the 
interior,  the  wall   being  formed  usually  by  a  single   layer  of 


.  229. — A  branch   <>i  .1  rul  mm- 

ing  tetn isp. .us.  .',  formed  bj  an 
interna]  cell  of  the  thallus  Mag 
nifiedabout  loodiam.  -AfterKUtz 

ing. 


228 


PLANT   LIFE. 


cells.      Mixed   with   the  spore-producing  cells,  however,  arc 
many  sterile  cells,  which   become  gradually  elongated,   and 


spm 


Fig 


-The  i 


phyte  of  a  peat  moss  {Sphagnum  acuti/blium)vntb  adjacent  parts 
of  thegametophyte.  The  spun  .phyte  consists  of  a  capsule,  -u'.  and  a  broad  foot,  sg",  At 
the  stage  shown  in  />'  it  is  still  completely  enclosed  in  the  tissues  of  the  gametophyte, 
viz.,  c,  the  enlarged  ovary  which  forms  the  calyptra  or  hood,  and  v,  the  vaginule  or 
sheath  surrounding  the  foot,  ar  is  the  neck  oi  the  ovary.  (Compare  fig.  331  I  The 
ajc  over  the  large-celled  central  tissue  (columella)  is  the  sporangium,  fit,  the  false 
stalk,  produced  by  the  gametophyte,  which  raises  the  sporopnyte.  [n  A,  the  calyptra 
has  broken,  only  a  fragment  remaining,  exposing  the  capsule.  '  d,  the  lid.  by  whose  fall 
the  sporangium  is  exposed  and  the  spores  escape.  ,  h,  leaves  oi  the  gametophyte  :  qt, 
the  false  stalk.  Compare  figs.  67,  72.  73,  in  which  the  stalk  is  part  oi  the  sporophyte. 
.  I  magnified  13  diam.;  /■'.  32  diam  — After  Schimper. 
FlG.  231. — Longitudinal  section  of  the  young  capsule  of  a  true  moss  (Bryum),  s,  spo- 
rangium. At  this  stage  the  mother  cells  01  the  spores,  spin,  have  become  free  (only  a 
few  are  shown  still  enclosing  the  spores):  tw,  the  wall  of  the  sporangium,  lined  by 
the  remains  of  another  layer  of  cells  now  disorganized  ;  <  ,  the  columella,  of  partly  col- 
lapsed cells ;  it,  intercellular  space  :  cm,  wall  of  the  capsule  :  .1  n,  the  annuius,  a  ring 
of  cells  which  pries  off  the  lid,  at  whose  edge  they  develop  :  ot,  the  outer,  in,  the  inner, 
peristome,  formed  by  the  thickening  of  parts  of  the  walls  of  certain  rows  of  cells;  >/.', 
nutritive  tissue,  with  chloroplasts  and  intercellular  spaces.  Magnified  25  diam. — Orig- 
inal. 


VEGETATIVE  REPRODUCTION.  229 

in  many  species  thicken  their  walls  along  one  or  more  spiral 
lines.  These  sterile  cells  are  called  elaters  (fig.  11,  A,  A'). 
They  serve  to  entangle  the  spores  in  dusters  when  they  are 
set  free.  The  sporangium  opens  at  maturity  by  splitting  at 
the  apex,  sometimes  into  two,  commonly  into  four  or  more, 
parts  (fig.  64). 

322.  Mosses. — In  most  mosses  the  sporangium  is  developed 
within  the  enlarged  upper  part  of  the  sporophyte,  to  which 
the  name  capsule  is  given.  In  the  peat  mosses  it  is  cap-  or 
thimble-shaped  (fig.  230),  while  in  most  of  the  true  mosses 
it  is  a  hollow  cylinder  (fig.  231).  It  opens  by  the  falling  off 
of  the  sterile  upper  end  of  the  capsule,  which  separates  as  a 
lid  and  thus  allows  the  spores  to  escape  from  the  upper 
end  of  the  cylindrical  sporangium.  By  the  time  the  spores 
are  mature,  the  sterile  central  tissue  of  the  capsule,  which 
forms  the  columella  (c,  fig.  231),  shrivels  and  often  almost 
disappears,  so  that  the  capsule  seems  to  be  a  cup  or  urn,  filled 
with  loose  spores.  In  the  younger  stage  (fig.  232)  the  orig- 
inal form  is  shown. 

323.  Ferns. — In  the  ferns  the  sporangia  are  usually  nu- 
merous, stalked,  free,  and  often  associated  in  clusters 
called  sori.  They  are  either  produced  upon  the  under  sur- 
face of  the  foliage  leaves  or  upon  specialized  leaves.*  The 
sori  are  often  arranged  in  elongated  clusters  or  lines 
(fig.  2$$).  Each  sorus,  or  a  (luster  of  them,  may  be  pro- 
tected by  a  special  outgrowth  from  the  cells  in  its  neighbor- 
hood, called  an  indusium  (tigs.  233,  234).  Each  sporangium 
consists  of  a  stalk  composed  of  two  or  four  rows  of  cells  ex- 
panding above  into  a  body  composed  of  a  single  outer  layer 
enclosing  the  spore  producing  cells,  and  at  maturity  the 
spores  themselves.  The  walls  of  a  row  of  cells  more  or  less 
completely  encircling  the  body  of  the  sporangium   become 

*  It  must  l>o  remembered  that  the  entire  plant,  consisting  of  root,  stem, 
and  leaves,  is  the  homologue  <>f  the  capsule  and  sialk  <>!'  the  mossworts. 


230 


PLANT    LIFE. 


irregularly  thickened  (sec  fig.  401).  The  strains  caused  by 
the  unequal  absorption  and  loss  of  water  burst  the  sporangium 
at  some  definite  point.  This 
Line  of  dehiscence  is  often 
between  a  pair  of  large  sad- 
dle-shaped cells  (fig.  401). 

324.  Sporophylls.  —  In 
many  of  the  ferns  the  leaves 
which  produce  sporangia  are 
not  different  from  the  foliage 


Fig.  233. 

Fig.  232. — Diagram  of  a  longitudinal  and  transverse  section  of  the  very  young  capsule 
of  a  true  moss  (Bryum).  The  transverse  section  is  taken  along  the  line  A  B.  a,  the 
mother  cells  of  the  spores  ;  < .  the  columella  ;  is,  intercellular  space.  The  constriction 
at  the  top  marks  the  limit  of  the  lid.  The  part  below  the  sporangium  is  the  neck,  with 
nutritive  tissues. — Original. 

Fig.  233. — A  leaflet  of  a  fern  (As/- id  in  in)  seen  from  the  back.  Eight  sori  are  shown, 
each  covered  by  its  own  indusium,  /.     Magnified  2  diam. — After  Sachs. 


leaves.  .  In  others,  certain  leaves  are  so  specialized  for 
bearing  the  sporangia  that  they  lose  their  nutritive  function 
in  part  or  entirely.  To  such  spe<  ialized  leaves  the  name 
sporophyll  is  applied. 

325.  Horsetails.  —  In  the  horsetails  the  sporangia  have  the 
form  of  sacs,  varying  in  number  from  six  to  twelve.  They 
arise  upon  the  lower  face  of  a  shield-shaped  sporophyll  (figs. 
235»  23())-  These  sporophylls  are  aggregated  in  a  close 
cluster    at    the  upper    end    of    the    axis,    constituting   what 


VEGETATIVE   REPRODUCTION.  2$\ 

may  be  called,  properly  enough,  a  flower.*  The  wall  of  the 
sporangium  when  young  is  formed  by  three  layers  of  cells, 
but  consists  at  maturity  of  one  layer  only,  which,  having  its 
cell-walls  thickened  in  an  irregular  manner  (fig.  238),  tears 
open  the  sporangium,  usually  along  a  vertical  line.  The  wall 
of  the  spore  consists  of  three  layers,  the  outer  one  splitting 
into  narrow  strips  and  remaining  lightly  attached  to  the  spore 
at  one  point  (fig.  239).  To  these  parts  of  the  cell-wall  the 
name  elaters  has  also  been  given.    (Compare  1"  321.)     Their 


Fig.  234. — Vertical  section  through  the  leaflet  shown  in  fig.  233,  passing  through  the  cen- 
ter of  a  sorus.  e,  ventral  epidermis;  <■',  dorsal  epidermis;  between  them  the  meso- 
phyll,  showing  3  veins  cut  across;  over  the  central  one  is  a  cushion  of  tissue  from 
whose  surface  arise  the  stalked  sporangia  s,  s.  i,  i,  the  indusium.  Magnified  about  30 
diam. — After  Sachs. 

purpose  seems  to  be  to  entangle  the  spores  so  that  they  may 
not  be  too  sparingly  distributed. 

326.  Club-mosses. — In  club-mosses  the  sporangia  are  sac - 
like  outgrowths  upon  the  upper  surface  of  the  leaf  near  its 
base,  or  occasionally  of  the  axis  itself  jusl  above  the  leaf. 
Sometimes  the  leaves  bearing  them  are  the  ordinary  foliage 
leaves  ;  in  other  species  they  are  specialized  and  crowded 
into  a  terminal  (luster  or  spike  (fig.   240). 

327.  Differentiation  of  spores. — Among  the  higher  fern- 
worts  tlie  spores  are  of  two  sizes  :  large  ones,  known  as  mega- 

*  This  term  is  not  generally  applied  to  those  sporophylls.  Rut  see  defi- 
nition of  a  flower,  %  320,  and  compare  tig.  237  of  a  "  flower"  of  Zamia. 


23: 


PLANT    LIFE. 


spore's,  and  much  smaller  ones,  known  rs  microspores  (fig. 
241).  Each  kind,  when  it  germinates,  produces  a  sexual 
plant,  or  gametophyte   (■   377),  upon  which,  however,  only 


Fio.  235. 


Ki<;. 


Fir,.  235  Pari  ol  two  sporophytes  ol  .1  horsetail  {Equisetum  arvense).  A,  the 
spring  shoots,  with  sheath  like  whorls  ol  leaves  below  and  crowded  sporophylls  above 
«,  summer  shoots,  much  branched,  with  inconspicuous  leaves;  nutritive  work  all 
done  by  stems  ..i  these  shoots.     Two  thirds  natural  size      After  Kerner. 

Fig.  236. — Three  sporophylls  from  the  flower  of  a  horsetail  {Equisetum  telmntein), 
seen  in  different  positions,  s,  the  shield-shaped  sporophyll ;  st,  its  stalk  attached  to 
the  center  of  dorsal  face  ;  sg;  sporangia.     Magnified  about  10  diam.— After  Sachs. 


one  sort  of  sexual  organs  is  borne.     The  megaspores  give  rise 
to  plants  bearing  female    organs    only,    the   microspores    to 


VEGE  TA  TI I 'E   RETROD  UC TION. 


233 


those  bearing  male  organs  only.  A  similar  separation  of 
sexes  in  the  gametophytes  frequently  occurs  when  the  spores 
are  equal  in  size,    as  in  Marchantia   and  horsetails,   but  it 


ri<;.  237. 

Fig.  237-  -A,  the  " flower "  of  a  seed  plant  (Zamia  muricata).  It  is  1  omposed  of 
crowded  sporophylls,  of  which  one  is  represented  in  A'  as  seen  from  the  side.     It  has 

a  stalk  capped  by  a  hexagonal  tup,  .>.  with  numerous  sporangia,   1  .  on  the  under  side. 
.  I ,  natural  size. '  ti,  magnified  about  6  diam      Aftei  Karsten, 
Fio.  23S. — A  bit  of  a  section  of  the  wall  of  a  sporangium  of  a  horsetail      The  cells  of 
the  outer  layer  thi<  ken  their  walls  along  spiral  lines.     The  two  inner  layers  of  CI 

become  disorganized  at  maturity  ol  the  sporangium.     Magnified  250  diam       \tt.r 

(  'ainpbell. 

I'll..  239.— Two  spores  of  a  horsetail  [Eguisetum  arvense);  one  showing  thi  elaters 
open,  as  when  dry,  the  other  with  them  coiled,  as  when  moist.  Magnified  25  diam. — 
After  Kerner. 


234 


PLANT   LIFE. 


always  occurs  when  they  are  unequal.  A  corresponding  dif- 
ference in  size  is  often  found  between  the  sporangia  con- 
taining small  spores  (microsporatigia)  and  those  containing 
large  spores  (megasporangia)  (figs.  241,  242  1. 

The  sex   terms,  male  and  female,  applicable  primarily  to 
the  sex  cells,  arc  applied  also  to  the  organs  and  to  the  plants 


240. 


Fig.  240. — Sporophyte  of  a  club-moss  (Lycopodium  clavatnm).  The  horizontal  stem 
is  densely  covered  with  leaves  ;  those  OB  the  erect  branch  become  small  and  few  tor  a 
space:  these  are  succeeded  by  broader  leaves,  the  sporophylls,  crowded  in  a  dense 
spike,  s.     Half  natural  size.— After  I'rantl. 

Fig.  241. — Section  through  three  sori  of  an  aquatic  femwort  {Salvinia  natans). 
Each  is  covered  by  a  double  indusium.  r,  /.  two  sori  consisting  of  sporangia  con- 
taining microspores  <see  tig.  242);  <».  a  sorus  consisting  of  sporangia,  each  containing 
one  megaspore.     M agnified  10  diain.     After  Sachs. 


which  bear  them,  so  that  the  microspores  are  said  to  produce 
male  plants,  and  the  megaspores  female  plants.  For  a  fur- 
ther account  of  the  gametophyte,  see  •    386,  394,  393. 

328.    Seed  plants.  —  In  the  seed  plants  this  differentiation 
of  the  spores   is  always    found.      The  microspores  are  called 


VEGE  TA  TI I  rE   REP  ROD  UCTION. 


235 


pollen,  and  the  megaspores  are  called  embryo-sacs  *  The  mi- 
crosporangia  and  megasporangia,  also,  are  always  different  in 
form  and  structure,  and  the  leaves  upon  which  they  are  usually 
borne  are  also  of  two  distinct  forms.  In  no  case  do  sporo- 
phylls  perform  nutritive  work;  they  are  always  specialized. 
Those  leaves  which  bear  microsporangia  are  called  stamens^ 
and  the  leaves  which   produce  the  megasporangia  are  called 


Fig.  242. — A,  a  microsporangium  of  Salvinia  seen  from  the  outside.  It  contain?;  (<^ 
microspores.  />',  four  spores  from  A,  surrounded  by  hardened  frothy  mucilage.  C, 
median  longitudinal  section  of  a  megasporangium,  showing  structure  oj  wall  at  matu- 
rity, and  the  single  spherical  megasporc,  with  its  proper  wall  (black  line)  and  a  thick 
frothy  epispore  ill  368).  A  and  C  magnified  55  diam.  B,  magnified  250  diam.— After 
Strasburger. 

carpels*  (figs.  245,  250,  251).  In  spite  of  these  special 
names,  it  must  be  carefully  borne  in  mind  that  the  sporangia 
and  sporophylls  of  the  seed  plants  are  not  different  from  those 
of  the  fernworts  or  mossworts  in  any  essential  particular. 

329.  The  sporophylls  of  the  seed  plants  are  usually  aggre- 
gated by  the  failure  of  the  internodes  of  the  axis  to  lengthen 
as  much  as  between  the  foliage  leaves.      Very  often,  also,  the 

*  These  special  names  were  given  because  the  seed  plants  were  first 
studied,  and  it  was  long  before  the  real  nature  of  the  pans  and  theii  n  la 
tion  to  similar  ones  in  the  lower  plants  were  known.  The  terms  are  still 
in  use,  and  are  likely  to  continue  to  be  used  for  convenient  e. 


236 


PLANT  LIFE. 


leaves  adjacent  are  modified  in  form  and  color  to  adapt  them 
to  securing  the  dispersal  of  the  pollen  by  various  agents, 
especially  insects.  Such  a  shoot  bearing  sporophylls  and 
accessory  leaves  is  called  a.  flower  (*\  330).  As  a  similar 
aggregation  of  the  sporophylls  occurs  in  horsetails  and  many 
club-mosses  (figs.  235,  240),  it  is  evident  that  the  flower  is 
not  distinctive  of  the  seed  plants,  though  it  attains  the  highest 
specialization  among  them.* 

The  parts  and   functions  of  the  flower  of  seed  plants  are 
now  to  be  discussed. 


The   Flower. 

330.  A  flower,  in  its  simplest  form,  may  consist  of  an  axis 
bearing  only  a  single  sporophyll  (fig.  243).  A  flower  usually 
consists  of  a  shortened  axis,  the  torus,  bearing  several  sporo- 
phylls and  several  accessory  floral  leaves  (figs.  104,  244). 


Fie    z43. 

Ho.   -M3-— -'.  a  single  flower  ;   /.',  a  portion  of  the  flower  cluster  of  A  risarum  r»/i,'<"''. 

The  flower  is  composed  of  one  stamen  only.      Magnified  slightly.— After  Kngler. 
Fir..  244-  A  Mower  of  linden,  halved;  showing  a  pestle-like  pistil.     Magnified  about  3 

diam. — After  Reiner. 

The  sporophylls  arc  known  as  essential  organs,  the  accessory 
leaves  as  the  perianth  and  bracts. 

The  essential   organs  are  of  two  sorts,  stamens  and  carpels. 
In  any  flower  they  may  be  all   stamens  or  all  carpels,  or  may 

*  It  is  for  this  reason  that  the  term  see  J  plants  is  preferred  to  Jlozuering 
plants. 


VEGETATIVE   REPRODUCTION.  237 

include  both  sorts  of  sporophylls.  The  perianth  may  be  com- 
posed of  one  or  two  kinds  of  Leaves,  often  bright-colored.    If 

there  are  two  sorts,  those  next  the  sporophylls  are  generally 
highly  colored,  and  constitute  the  corolla.  Each  leaf  of  the 
corolla,  when  distinct,  is  a  petal.  The  leaves  below  the  co- 
rolla are  often  green.  They  constitute  the  calyx,  and  each, 
when  distinct,  is  a  sepal. 

331.  Carpels.  —  The  leaves  (sporophylls)  bearing  the 
ovules  (megasporangia)  are  called  carpels.  They  ma\  In- 
flattened  ;  or  so  curved  that  in  the  course  of  their  develop- 
ment the  edges  unite  and  a  cavity  is  more  or  less  perfectly 
enclosed;  or  neighboring  carpels  may  grow  together  in  such 
a  way  as  to  form  a  case.  Such  hollow  structures,  whether 
composed  of  one  or  more  carpels,  are  often  somewhat  pestle- 
shaped,  whence  they  early  received  the  name  pistil  (fig.  244). 
A  flower  whose  only  essential  organs  are  pistils  is  called  pis- 
tillate.  The  sporangia  arise  usually  upon  the  ventral  (inner) 
face  or  the  edges  of  the  carpels.  In  the  open  carpel  they  are 
exposed,  but  in  the  closed  carpels  they  are  completely  shut 
in,  except  for  a  narrow  opening  which  sometimes  remains,  by 
which  the  interior  cavity  communicates  with  the  outside  air. 

332.  Ovules. — Among  seed  plants  the  sporangia  which  the 
carpels  bear  are  universally  known  as  ovules,  a  name  given  to 
them  under  the  supposition  that  they  were  the  eggs  which, 
upon  fertilization,  produce  new  plants.  Though  they  are  not 
in  any  respect  comparable  to  the  real  eggs  (since  the)  are 
produced  by  the  non-sexual  or  sporophyte  phase),  the  name 
is  retained  for  convenience. 

333.  Gymnosperms  and  angiosperms. — When  the  changes 
through  which  the  ovule  passes  are  complete,  it  bee  nines  the 
seed.  When  the  ovules  are  produced  upon  the  free  stirfai  e  of 
an  open  carpel,  the  seeds  are,  therefore,  exposed.  On  the 
contrary,  when  the  ovules  are  borne  within  a  closed  pistil 
(formed    by  one    or   mure    carpels)  the   seeds    are   developed 


238 


PLANT   LIFE. 


within  this  case,  by  which  they  are  protected  until  mature,  or 
longer. 

These  two  methods  of  seed  pioduction  form  the  basis  for 
the  separation  of  the  seed-bearing  plants  into  two  great  groups, 
one  known  as  gymnosperms,  or  plants  with  naked  seeds,  the 
other  as  the  angiosperms,  or  plants  with  encased  seeds. 
Open  carpels  are  found  exclusively  among  the  gymnosperms, 
to  which  belong  the  cone- bearing,  mostly  evergreen,  trees, 
while  the  closed  pistils  are  chiefly  found  among  angiosperms, 
to  which  belong  the  majority  of  garden  and  field  plants  and 
the  deciduous  forest  trees. 

334.  The  simplest  form  of  carpel  occurs  in  Cycas  (fig. 
245),  in  which  the  ovules  are  borne  on  the  edges  near  the 
bases  of  leaves  which  somewhat  resemble  the  foliage  leaves, 
and  form  a  whorl  between  preceding  and  succeeding  whorls 
of  foliage  leaves  upon  the  main  axis.  The  carpel  of  most 
gymnosperms  is  a  scale  from 
whose  upper  surface  arises  a 
similar  fleshy  scale,  the  pla- 
centa, bearing  two  ovules 
upon  its  ventral  (upper  or  in- 


FlG.  245.  Fir..  246. 

Fig.  245. — An  ovule-bearing  leaf  or  carpel  of  Cycas  r*wfl/Kfa,  showing  4  ovules  near 
base,  replacing  the  1t.uu  lies.  (  hi  the  right  above,  a  young  seed.  About  one  qu  liter 
natural  size.— After  Sachs. 

Fk;  246 —A  young  cone-scale  (placenta)  of  Scotch  pine  showing  the  two  ovules;  the 
latter  halved  parallel  to  the  scale,  showing  the  body  of  ovule  and  the  prolonged  integ- 
ument forming  the  micropyle,  in.  The  scale  is  attached  at  /».  Magnified  about  8 
diam.     After  Kerner. 


VEGETA  TIVE    REP  ROD  I  rC2  'ION. 


239 


ner)  face  (fig.  246).  In  such  cases  the  carpels  are  generally 
aggregated  in  close  spirals  near  the  end  of  a  thickish  axis, 
and  finally  ripen  into  a  cone  (tigs.  341,  358),  which  gives 
the  name  to  one  of  the  largest  orders  of  gymnosperms,  the 


Fig.  247. — .-/,  shoot  <>f  the  yew  ( lux  us  baccata)  with  three  ripe  seeds,  each  surrounded 
by  a  fleshy  aril.  Natural  size.  B,  ovule  with  its  tip  projecting  from  the  scale  leaves 
dt  the  shoot  it  terminates.  (  .  the  same,  halved,  showing  the  body  of  ovule  (sporan- 
gium] and  the  lone;  tube-like  integument.  O,  young  seed  ol  same,  with  aril  partly 
formed.  E,  mature  seed,  halved.  The  central  (white)  body  is  the  embryo;  around 
it  (dotted)  the  food ;  then  the  seed  coat;  then  the  aril  (white!.  A',  C,  /'.A',  slightly 
magnified. — After  Kemer. 


Conifers.  (See  further  ^|  404.)  The  ovules  of  some  gym- 
nosperms are  not  borne  by  carpels,  but  each  terminates  an 
axis,  as  in  the  yew  (fig.  247). 

335.  The  closed  pistils  of  angiosperms  are  usually  distin- 


240 


PLANT  LIFE. 


guishable  into  (i)  an  enlarged  basal  part,  the  ovular?,*  con- 
taining the  ovules,  surmounted  by  (2)  a  slender  part  of  vari- 
able length,  the  style,  which  is  terminated  by  (3)  a  rough, 
sticky,  or  branched  part,  the  stigma.      (See  figs.   250,  258.) 

336.  The  stigma  may  take  the  form  of  a  knob,  a  ridge, 
a  straight  or  wavy  line,  or  be  lobed  or  branched.  However 
compact,  it  is  usually  roughened  by  the  prolongation  of 
its  surface  cells  into  rounded,  pointed,  or  hair-like  exten- 
sions (figs.  248,  283),  which  frequently 
secrete  a  sticky  fluid.  Its  purpose  is 
to  secure  the  adhesion  of  the  pollen 
spores  brought  to  it  by  various  agents, 
among  the  most  important  of  which  are 
the  wind  and  insects. 

337.  The  style  may  be  thick  or 
slender,  long  or  short,  branched  or  un- 
branched,  hollow  or  solid.  It  is  fre- 
quently wanting,  so  that  the  stigma  is 
said  to  be  sessile  upon  the  ovulary. 

338.  Simple  and  compound  pistils. 
^fromV^gl*!   com  —When  several  carpels  are  present  in 

toCSchZr£"&i  f^'Cd!  one  flower  the>'  may  form  as  many 
ZSL^&vFSaZ  separate  simple  pistils  as  there  are  car- 
#ft&ffi£E-£  P<*s.  ^  numerous,  the  axis  will -be 
After  straslurger.  enlarged  or  elongated  to  accommodate 

them.      (See  ^[    360.)      Instead  of  forming   separate   pistils, 


*  This  part  was  early  called  the  ovary  (a  name  which  is  still  in  general 
use),  meaning  the  organ  which  produces  eggs,  under  the  impression  that 
the  ovules  (  =  little  eggs)  were  like  the  eggs  of  birds,  an  idea  which  was 
further  carried  out  in  the  name  albumen  given  to  the  fond  stored  in  the 
seed.  (See  ' ,T  403,  407. )  To  avoid  confusion  with  the  true  ovary  (1  388), 
in  which  the  real  egg  is  produced  (^  387),  I  here  suggest  the  name  ovu- 
lary— i.e.,  the  organ  which  produces  ovules.  The  word  ovule,  though  as 
had  in  etymology  as  ovary,  is  convenient,  and  does  not  lead  to  any  con- 
fusion. 


V EG  ETA  TIVE   RE PROD  UCTION. 


24I 


the  carpels  may  be  united  to  form  a  single  compound  pistil. 
This  union  is  commonly  brought  about  (1)  by  the  actual 
growing  together  of  the  parts  in  a  very  young  stage,  so  that 
the  cells  interlock  and  become  partially  or  completely  united; 
or  (2)  the  carpels  develop,  not  as  separate-  parts,  but  as  a 
ring  of  tissue  growing  up  from  the  surface  of  the  axis;  or, 
(3),  a  portion  of  each  carpel  develops  separately,  and  later 
these  distinct  parts  may  be  lifted  by  the  growth  of  the  ring 
of  tissue  beneath  them  (fig.  249). 

339.   The  union  *  of  the  carpels  may  be  only  at  the  base  ; 
or  it  may  involve  the  entire  ovulary,  leaving  the  styles  free; 


Fig.  249.  Fig.  250.  Fir,.  251. 

Fig.  249.  —  Pistil  of  white  hellebore  (Veratrwn  album)  showing  time  carpels  separate 

above  only.      Magnified  about  <•  diam.      After  llerg  and  Schmidt. 
Fig.  250. — Calvx  and  pistil  of  the  manna  ash  (Fraxinus  ornus)  showing  calyx   leaves 

united  at  base  and  carpels  united  throughout,  the  slightly  2-lobed  stigma  only  giving 

external  evidence  of  their  number.    Magnified  several  diam.— After  Berg  and  Schmidt. 
Fig.  251.— Pistil  of  white  potato  halved  transversely,  showing  two  carpels  united  at 

center  where  their  edges  form  ,1  large  placenta  on  whose  surface  the  ovules  arise. 

Magnified  several  diam— After  ICeraer. 

or   the  union   may  be  complete,  with  the  exception  ot   the 

stigmas,  or  it  may  involve  even  them  (tig.  250).  Union  may 
take  place  in  such  a  way  that  the  edge  of  each  carpel  meets 
its  fellow  and  the  edges  of  neighboring  carpels  in  the  center 
of  the  compound  pistil  (fig.  251).     In  this  case  the  ovulary 

*  This  phrase  may  It  used  for  convenience  in  all  cases,  oven  of  those 

pistils  in  which  the  carpels  were-  at  no  time  separate, 


24- 


PLANT  LIFE. 


is  divided  into  as  many  chambers  as  there  are  component 
carpels,  and  the  partition  by  which  the  chambers  are  sepa- 
rated represents  the  adjacent  parts  of  the  two  carpels.  Or 
the  carpels  may  unite  with  each  other  at  their  edges  only,  so 
-rr'sr-^^Tj^s,  that  the  line  of  union  is  at  the  outside 
^^s— cg^l^^^  of  the  pistil.  In  this  case  the  ovulary 
will  have  a  single  chamber.     In  both  these 

FlG.     252. — A     transverse  . 

section  of  the  capsule  of  methods  of  union  the  normal  number  of 

shepherd's  purse.    The      , 

pistil  consists  ,,f   two  chambers  in  the  ovulary  may  be  increased 

carpels,  at  whose  united 

edges  two  placenta:  are    by     OlltglOWths     from     the     Carpels     them- 

formed     carrying     the 

ovules  (now  seeds).  The  selves,  as  in  figure  252,  where  Jrom  the 

partition  from  one  pla- 
centa to  the  other  is  an  united  edges  of  the  carpels  a  plate  of  tis- 

outgrowth    (false    parti- 
tion) and  not  part  of  the   sue  has  grown  out   to  meet  a  correspond- 

carpel.   Magnified  about 

6  diam.— After  Bessey.  ing  one  from  the  other  side,  so  that  what 
should  be  a  one-chambered  pistil  has  become  two-chambered. 
(Compare  also  fig.  276.)  Even  simple  pistils  are  subject  to 
such  subdivision  of  their  interior  (fig.  253). 


Fig.  253.  Fig.  254. 

Fig.  253. — Lower  half  of  the  pistil  of  Astragalus  canadensis.  It  consists  oi  only  one 
carpel,  but  is  divided  into  two  chambers  by  a  false  partition,  an  outgrowth  from  the 
midrib  of  the  leaf.      Magnified  several  diam  —  Alter  dray. 

Fig.  254— Two  stages  in  the  development  of  the  ovule  of  the  currant,  ./.a  median 
longitudinal  section  ol  a  young  ovule;  n,  the  sporangium;  //.inner  integument  be- 
ginning to  develop  as  .1  nng  at  base  oi  n  ;  .'/,  the  fundament  of  the  outer  integument ; 
»r,  the  mother  cell  of  the  niegaspores  ;  /,',  a  similar  section  of  tin  sporangium  alone, 
older,  showing  »/',  ;//",  «/'",  the  daughter  cells  of  m  ;  ///'".  only  becomes  a  perfect 
spore;  m'  and  m1'  do  not  develop  further  and  become  destroyed.  Contents  of  cells 
not  shown.     Magnified  350  diam. — After  Warming. 

340.  Ovules. — An    ovule    consists  of  a    megasporangium 
partially  enveloped  by  one  or  two  outgrowths  from  beneath. 


VEGETATIVE   REPRODUCTION.  243 

The  sporangium  forms  the  body  of  the  ovule  (fig.  254).  In 
the  interior  the  mother  cells  of  the  megaspores  are  differen- 
tiated early,  the  outer  tissues  forming  the  wall  of  the  sporan- 
gium (fig.  254).  In  a  few  ovules  as  many  as  20  to  40  mega- 
spores begin  to  develop  ;  in  most  only  one  to'  four.  Even 
when  several  megaspores  begin  to  form  it  is  rare  for  more 
than  one  to  reach  perfection  ;  the  remainder  disappear 
almost  completely. 

341.  Indehiscence. — The  megaspore  never  escapes  from 
the  sporangium  ;  a  condition  which  necessitates  many  adapta- 
tions. (See  further  «r  358,  414).  The  protection  of  the 
megaspore  by  the  sporangium  renders  a  thick  wall  unneces- 
sary. For  this  reason  the  megaspore  looks  more  like  a  cavity 
in  the  ovule  than  like  a  spore.  Because  an  embryo  appears 
later  inside  this  apparent  cavity,  the  megaspore  of  seed  plants 
has  long  been  called  the  emhryo-sac. 

342.  Integuments. —  The  sporangium  is  surrounded  by 
one   or   two    integuments.      These  arise  as  outgrowths   from 

the  tissues  adjacent.      If  the   spo-  ^-^ w 

rangium  is  to  have  two  coats,  the        *r*     |  L 

inner   appears    first    as   a    low    ring        A,      V  /'/'■Jf""'      I 

around  its  base   gradually  growing  ,      ^"y 

up    around    it  ;    the    outer    shortly  ,  ^^^ 

appears  in  the  same  way  (fig.  255). 

_,  .  11  1        Fig.  255.— Two  very  young  ovules 

I  hese   integuments,  as  well  as  the     of  the  California  puppy  ,/„/,. 

scholtzia  I,  seen  from  the  outside. 
sporangium,     often     grow     unsvm-      /•'.  somewhat  older  than 

.  '.  the  sporangium ;  fc,  the  inner  in- 

metncally,  so    that    at    the  maturity      tegument;  /■>■,  the  outer  integu 

ment;  ///,  the  -ulk.      Magnified 
Of  the  megaspore  the  OVUle  is  Often       [4odiam       Mtei  Duchartre. 

variously  curved  (figs.  254,  255,  256).  The  megaspore  it- 
self may  be  distorted  by  this  means  so  as  to  lose  still  more 
its  likeness  to  a  spore. 

343.  Location. — Ovules  are  borne  either  upon  the  axis 
itself  or  upon  the  carpels.  When  they  are  borne  upon 
the    axis    they    may    be    either    uncovered,    as    in    the    yew 


244 


PLANT  LIFE. 


among  gymnosperms  (fig.  247),  or  the  carpels*  may  form 
a  covering,  as  in  angiosperms.  In  these  plants  the  ovule 
may  terminate  the  axis,  as  in  sunflower  and  buckwheat 
families  (fig.  257);  or  the  ovules  may  be  lateral  upon 
the  surface  of  an  enlargement  of  the  axis  within  the  ovulary, 
as  in  pinks  and  primroses  (fig.  258). 

It  is  usual,  however,  for  the  ovules  to  arise  upon  a  carpel, 
either  singly  or  in  clusters  which  occupy  definite  portions  of 
its  surface.  The  cushion  or  ridge  from  which  the  ovules 
arise  is  called  the  placenta.     In  the  pines  the  placenta  is  a 


Fir;.  256. — Diagrams  of  median  longitudinal  sections  of  three  sorts  of  ovules  to  show 
curvatures  due  to  unsymmetric  growth.  A,  a  straight,  />',  an  inverted,  C,  a  bent  ovule. 
In  all:  _/,  the  stalk;  X-,  the  sporangium;  //,  the  inner  integument;  at,  the  outer  in- 
tegument;  m,  the  micropyle ;  c,  the  base  of  the  sporangium  where  the  integuments 
arise  (called  the  chalaza);  r,  the  ridge  (rhaphe)  formed  by  the  union  of  stalk  and  outer 
integument ;  em,  the  megaspore.  As  C  develops  further  em  may  become  sharply  bent 
on  itself.— After  l'rantl. 


scale-like  outgrowth  from  the  upper  surface  of  the  carpel, 
bearing  two  ovules  (fig.  246),  and  as  the  cones  mature  these 
gradually  outgrow  the  carpels  and  constitute  the  main  por- 
tion of  tlie  ripened  cone.     To  such  placentas  the  ovules  are 

attached  by  one  side  ;  they  are  therefore  entirely  sessile.     The 


•Although  the  enclosing  leaves  in  this  case  do  not  bear  the  sporangia, 
and  are,  therefore,  not  strictly  sporophylls,  their  similarity  in  form  renders 
it  convenient  to  retain  the  name  carpel  even  for  those  pistils  in  which 
they  are  a  mere  roof  over  a  convex  or  hollowed  axis  bearing  the  ovules. 
(See  fig.  25S.) 


VEGETA  TIVE   REPRODUCTION. 


••15 


placenta  in  angiosperms  commonly  consists  of  a  cushion  of 
tissue  usually  at  the  united  edges  of  the  carpel  or  carpels,  [f 
the  carpels  are  united  into  a  compound  pistil,  the  placentas 
will  be  cither  isolated,  as  ridges  upon  the  inner  face  of  the 
wall  of  the  ovulary  (fig.  25 2 J, 
or  aggregated  at  its  center 
(fig.  251).  Occasionally  the 
ovules  arise  upon  the  entire 
inner  face  of  the  carpels,  as  in 
the  gentians. 


Fig.  257. 


Fig.  258. 


Fig.  257.— A  median  longitudinal  section  through  the  flower  of  Klu-um  undulatutn, 
s,  a  sepal;  /.  a  petal;  n.  a,  n,  anthers;  «,  stigma;  /.  ovulary;  kk,  sporangium, 
which,  with  the  two  integuments  over  it,  forms  the  single  ovule  terminating  the  axis ; 
</>;  nectary      Magnified  about  10  diam. — After  Sachs. 

Fig.  258.  -Pimpernel  lAmtgnUu  arvensis).  A,  median  longitudinal  section  ol  a 
young  flower-bud ;  /.sepal;  c,  corolla,  just  beginning  to  develop ;  .(.anther;  A",  car- 
pels growing   over  A.   tne   apex   ol    the   axis.      />',  median   longitudinal  section  ol    the 

pistil.    . .  the  carpels,  forming  a  root  over  S,  the  axis  on  which  ovules  are  beginning 

to  develop,  and  growing  up  to  form  a  columnar  style  at  whose  apex  is  the  stigma,  '.. 
(',  the  same,  older.  ,S,  the  enlarged  apex  of  the  axis  showing  six  ovules,  Sk,  in  sec- 
tion; gr.  the  style:  n,  the  stigma,  on  which  arc  lodged  pollen  grains,  p.  All  magni- 
fied.—After  Sachs. 


344.  Stamens.— A  stamen  is  a  leaf  (sporophyll)  of  the 
seed  plants  which  bears  the  microsporangia,  or  pollen  sacs. 
The  flowers  whose  essential  organs  are  all  stamens  are  said  to 


246 


PLANT  LIFE. 


be  staminate.  Rarely  a  single  stamen  constitutes  a  flower. 
Except  for  the  crowding,  the  stamens  are  arranged  like  all  the 
other  leaves  of  the  plant,  arising  on  the  axis  alternately,  or 
in  one  or  more  circles.  The  stamens  exhibit  great  diversity 
of  form  and  size.  Each  usually  consists  of  two  parts,  a  stalk, 
called  the  filament,  bearing  an  enlarged  portion,  called  the 
anther. 

345.  The  filament  may  be  long  or  short,  slender  or  thick, 
rounded  or  flattened.  It  may  be  entirely  wanting,  in  which 
case  the  anther  is  sessile. 

346.  The  anther  is  usually  larger  than  the  filament  and 
commonly  two-lobed,  having  the  sporangia  located  in  the 
thicker  parts.  The  sterile  tissue  between  the  sporangia  is 
called  the  connective  (fig.  262).  This  appears  usually  as  a 
mere  continuation  of  the  filament,  but  sometimes  is  prolonged 
beyond  the  body  of  the  anther,  as  an  appendage  (fig.  259). 


Fig.  260. 

Fi<;.  259. — Anther  of  the  sweet  violet  (Viola  odor,tta),  showing  the  connective  pro- 
longed into  a  triangular  tip.      Magnified  about  5  chain-  After  Knurr 

I  ig  - \  ut  1 1.1  of  thyme  (  Thytnui  serpyllum),  showing  broad  connective.  Magni- 
fied about  5  diam. — After  (Center, 

I'M..  261. — Anther  of  the  sage  {Salvia  <>/'//,  inalis).  Opposite  a  the  filament  proper  is 
jointed  to  the  elongated  connective  which  has  one  perfect  anther-lobe  on  the  upper 
end;  on  the  other  the  sporangia  do  not  develop.  Magnified  about  5  diam.— After 
K,  enter. 

It  is  sometimes  broad,  so  that  the  sporangial  lobes  are  widely 
separated  (fig.  260),  and  may  even  be  so  long  and  slender  as 
to  seem  a  part  of  the  filament  (fig.  261). 


VEGE  TA  TIVE   REP  ROD  UCTIOM. 


M7 


347.   Sporangia.— The   anther   bears    from    1-12    micro- 
sporangia  upon  its  surface,  or  wholly  or  partly  sunk  in   its 


Fig.  262.— Transverse  section  of  the  anther  of  thorn-apple  (Datura  Stramonium). 
c,  connective,  with  a  small  stele  embedded  in  parenchyma  ;  a,  />,  a,  /,  the  four  spo- 
rangia, arranged  in  pairs  showing  pollen  grains.  When  the  sporangia  break,  the  walls 
rupture  at  the  groove  between  a  and  /.     Magnified  about  25  diam.  —After  Frank. 


tissues.      In   most  anthers  the  sporangia  are  either   2  or  4 

(fig.  262).      When  there  are  four  they  are  often  paired,  and 

each  pair  may  become   confluent  by 

the  absorption  of  the   portion  of  the 

anther  tissue  between  them  (fig.  263). 

This  occurs  about  the  same  time   that 

the  outer  wall  bursts  in  order  to  set 

free  the  spores.      Such  anthers,  at  the 

time  of  opening,  are  apparently  two- 

chambered.      In  those  which  contain 

only  two  sporangia,  the  two  may  open  Fig.  263. -Trans verse  section  of 

.  .  bursted    anther   of    a    lily   (Bu- 

independently,    or   they   may   become    tomus umbeiiatus).  Sporangia 

n  ,  ,  have  ruptured  at  z,  so  th.it  the 

confluent,     so     that     at     maturity     they     two  pairs  have  each  formed  a 

single  cai  itv.    The  coi 
may     seem      to      constitute      a      single     is  relatively  small;  in  the  centei 

a  single  stele.    Magnified  about 
chamber.  2odiam.     mm  Sachs 

348.   Dehiscence. — The  opening  of  the  1  hambers  occurs  in 

one  of  three  ways  :   by  pores,  by  slits,  or  by  valves.    (1)  A  small 

area  of  the  outer  wall  is  absorbed  or  breaks  away  so  that  the 


248 


PLANT   /.//■/■:. 


pollen  spores  sift  out  through  the  pore  so  formed  (fig.  264)  ; 
or  (2)  a  crack  begins  at  one  point  and  extends  lengthwise  of 
the  sporangium,  in  which  case  the  anther  is  said  to  open  by 
slits  (figs.  259,  260,  261)  ;  or  (3)  the  break  occurs  along  a 
line  considerably  curved,  and  the  flap  (valve)  thus  loosened 
curls  up  or  lifts  so  as  to  allow  the  escape  of  the  spores  (fig. 
265).      All  three  methods  are  dependent  upon  some  special 


Fig.  265. 


Fie.  264. — Anther  and  pollen  of  a  Rhododendron.  A,  the  anther,  opening  by  pores  at 
the  end  and  allowing  the  pollen  to  escape.  Magnified  8  diam.  //.pollen  grains  ad- 
herent in  four-,  (tetrads)  as  formed  in  the  mother  tells:  the  tetrads  an-  held  together  by 
a  stirkv  material  which  draws  nut  i  1 1 1 . .  cobwebby  threads  as  they  are  separated.  Mag- 
nified 50  diam. —  After  Kernel 

FlG.  205.  A  flower  oi  cinnamon,  halved.  The  calyx  and  stamens  are  raised  on  a  cup 
developed  around  the  pistil.  The  anthers  open  bj  uplifted  valves,  one  for  each  spo- 
rangium, which  lure  are  arranged  in  two  stories  instead  of  in  pairs  side  by  side.    Mag- 

nilied  about  7  diam.  —  After  1. 


structure   of  the  wall  of  the  sporangium   at  the  lines  of  rup- 
ture. 

349.  Union. — The  stamens  are  not  infrequently  united 
with  each  other  or  with  some  of  the  neighboring  leaves  of 
the  flower.     They  may  l>e  united  to  ea<  h  other  by  their  fila- 


i "/•/<//•;  ta  ri i  •/•;  retrod  uction. 


249 


merits  only,  or  by  their  anthers  only,  or  throughout  their 

whole  length.  Union  with  the  pistil  or  pistils  is  rather  un- 
common, but  union  with  the  corolla  or  calyx  is  very  frequent. 
The  union  of  stamens  may  be  real  or  apparent.  They  may 
develop  independently  anil  later 
cohere  by  their  adjacent  edges 
(fig.  266).  Or  they  may  begin 
development  separately  and  be 
subsequently  raised  by  the  growth 
of  a  ring  of  tissue  of  the  torus 
(•[360),  so  that  the  free  portions 
arise  from  the  top  of  a  shorter  or 
longer  tube.  "When  the  stamens 
and  corolla,  arising  independently, 
are  carried  up  together  by  the 
growth  of  such  a  zone  of  the  axis, 
the  stamens  appear  to  arise  from 
the  surface  of  the  corolla  (fig. 
267). 

350.  Branching.  —  The  sta- 
mens frequently  branch,  and  this 
is  difficult  to  distinguish  from  the 
displacement  by  basal  growth  just 
described,  except  by  studying 
their  development.  When  sta- 
mens branch  a  single  fundament  appears,  on  which  later  arise 
smaller  knob-like  elevations,  the  fundaments  of  the  branches, 
each  with  its  own  growing  point.  (See  figs.  268,  269,  270; 
also  •  171  and  figs.  146,  166  on  branching  of  loaves,  of 
which  this  is  only  a  spe<  ial  case.) 

351.  Pollen  grains. — The  microspores  produced  in  the 
sporangia  of  the  stamen  are  at  maturity  single  cells.  Their 
forms  and   walls    are   various,   being   round,   ovoid,    or   even 

angular,  with  the  surface  smooth,  grooved,  or  roughened,  with 


sunflc 


The  stamens  of  one  of  the 
family  (Cosmos  bi/>hi- 
natus).  A,  stamen  tube  formed  by 
five  stamens  coherent  by  their  an- 
thers around  the  style;  the  fila- 
ments with  a  tuft  of  hairs  about  the 
middle.  />'.  the  same,  but  stamens 
only;  the  tube  has  been  slit  along 
one  side  and  opened  out  Hat;  seen 
from  the  inside,  Connective  pro- 
longed; dehiscence  by  slits  Mag- 
nified about  7  diam.    After  Baillon. 


PLAiXT   LIFE. 


few  or   many   bosses,  points,    or    ridges,   as    in    other  spores 
(A-D,  fig.  271).      In  the  pines  the  outer   layer  of  the   wall 


G'g-^s 


Kig   1*67.  Fig.  269. 

Fig.  267. — Corolla  of  Alcanna  tinctoria  slit  and  laid  open,  showing  almost  sessile 
stamens  united  with  corolla  above  the  middle  of  tube,  s,  scale-like  outgrowth  from 
corolla.  The  tube  between  .v  and  the  notches  at  edge  of  corolla  result  from  the  growth 
of  a  ring  of  tissue  beneath  the  five  fundaments  of  the  corolla  which  produce  the  five 
corolla  lobes  c.  Having  grown  so  tar,  a  ring  of  tissue  inside,  on  which  the  stamen  fun- 
daments were  developing,  became  involved  in  this  upward  growth,  and  thus  the  sta- 
mens were  carried  up  and  arise  just  above  j.  Magnified  4  diam. — After  Berg  and 
Schmidt. 

Fig.  268.  -Very  young  flower  of  Hypericum  perforatum,  seen  from  above,  showing 
s,  sepals;  /•,  fundaments  of  petals  ;  a, a, a,  fundaments  of  the  three  stamens,  each  al- 
ready with  two  lateral  growing  points,  the  fundaments  of  branches,  appearing;  g;  fun- 
daments of  3  carpels.  Compare  with  figs.  269  and  270.  Magnified  about  50  diam. — 
After  Frank. 

Fig.  269,  An  older  stage  of  fig,  268,  showing  only  the  fundaments  of  stamens,  a,  and 
of  carpc-K.  g:  <  in  the-  latter  at  the  angles  appear  the  fundaments  of  the  three  styles. 
Many  branches  of  a  have  begun.  Compare  tig.  270.  Magnified  about  50  diam. 
— After  Frank. 


forms  two  bladdery  swellings  which  make  the  spore  relatively 
lighter  (E,  fig.  271).  The  pollen  spores  arise  in  the  spo- 
rangia in  fours  in  each  mother  cell,  as  described  in  ^j  306. 
(See  also  fig.  264.)      They  are  either  dry  and  powdery  when 


VEGETA  TIVE   REPRODUCTION. 


251 


ng    to 


the  sporangia  burst,  or  are  mois 

each  other    in   larger  or   smaller 

clusters    (fig.    264).      Sometimes, 

as  in  orchids  and  milkweeds,  they 

are  all  held  together  in  one  mass 

by  the  remnants  of  the    mother 

cells  in  which  they  were  formed, 

and  are  attached  to  a  part  of  the 

tissue  of  the  anther  which  carries 

the  mass  as  a  stalk  or  handle  (figs. 

272,  273).     Dry  spores  are  usually  FlG 

adapted  to  distribution  by  wind;     fSSdtf-^lf^o? 

while     the    adherent    spores    are     t^t^T^^t^. 

adapted  to  carriage  by  small  ani-     L%^FraMkagnified  ab°Ul  3  ***' 

mals,  especially  insects.       (See  further^]"  481.) 

352.   Germination  in  place. — By  the  time  the  sporangia 


270.  -  Mature   condition  of   the 


Fig.  271.— Pollen  grains.    A,  white  water  lily  (Nymf  h ten  alba).    B,  a  thistle  (Ctrswm 
>ii-mo>aU-).     C.a  mallow  {Hibiscus  ternatus).     D,  dandelion  {Tat 
cinale).     Magnified  200  diam.— After   Kerner.     E,  pine,  showing  bladdery  enlarge- 
ments, *,*,oi  the  outer  layer  of  the  cell-wall.    The  central  portion  is  the  body  of  the 

spore   filled   with   protoplasm   with  a  large   nucleus.      Kroin   it  is  separated  a  lenticulai 
cell,  /'.  the  rudiment  ot  tile  gainetuphyte.      Magnified  400  diam  -Alter  Strasburgei 


are  old  enough  to  release  the  spores,  the  latter  have  already 
germinated  and  begun  to  form  a  new  sexual  plant,  the  male 
gametophyte.     Thus  the  spores  of  the  non-sexual  plant  give 


252 


PLANT  LIFE. 


rise  to  a  plant  of  the  other  or  sexual  phase  ;  the  sporophyte 
produces  the  gametophyte.  (For  a  description  of  the  plant 
thus  formed  see  *  3 85.) 

353.   Perianth. — The    perianth    is    not    present     in    any 


Fig.  272. — A,  hanging  flower  of  milkweed,  seen  from  the  side.  The  petals  are  sharply 
reflexed.  Natural  size.  />,  the  upper  part  of  same,  magnified  about  2}  diam.,  with 
two  of  the  appendages,  ,/.  ol  the  stamens  cut  off  and  the  front  of  the  anther  wall  dis- 
sected away  to  show  its  two  pollen  masses.  C,  two  pollen  masses  from  neighboring 
anthers  connected  to  a  dip,  by  which  they  may  be  attached  to  the  foot  of  an  insect. 
Magnified  about  S  diam.  /».  foot  of  an  insect  with  pollen  masses  attached.  In  (and 
D  the  pollen  masses  are  inverted  as  compared  with  their  position  in  .  /  and  /•'. — After 
Kerner. 


gymnosperms  (^[  2,2,2,),  except  in  a  rudimentary  form  in  a 
few  species  of  the  highest  order.  In  angiosperms  the 
perianth,  which  is  rarely  wanting,  is  primarily  for  the 
protection  of  the  sporophylls.  As  in  all  cases  where  leaves 
are  produced  rapidly  and  in  dose  proximity  on  a  short 
axis,  they  grow  during  their  earl]  Stages  more  rapidly 
upon  the  outer  face  than  the  inner.  They  are,  therefore, 
concave  inward  and  closely  pressed  together,  forming  a  hud. 
At   a  certain  stage   the  growth   upon    the  two   faces  of  the 


VEGETATIVE   REPRODUCTION.  253 

perianth    becomes  equal,  and   later   is  more   rapid   upon   the 

inner   face  than  the  outer.      At  this  time  Jt$$b> 

the  flower  unfolds,  the  perianth  spreading  Jf     ^$$ 

more   or   less  and   exposing  the  stamens  jpjr 

and   pistils  within.      These  variations  in  g  ^^  ctl 

growth  are   often  repeated,  the  stimulus  ^fT 

being  light  or  heat  or  both,  when   it  is  Fic.273 -Pollen massfrom 

,1  an    orchid.        The   pollen 

necessary  to  protect   the   spores  against      gndns  are  arranged  in 
unfavorable  weather.      Such  flowers  open      legated  at 7heCendr<ofga 

j      1  ,    .  •  \      c  ii      •     1  stalk,   cd,  terminating  in 

and  close  several  times  before  their  leaves      an  enlarged  sticky  disk, 

.  ,  /c,  ,        w      oei   \  e.bymeansof  which  the 

wither.      (See  also  %  286.)  p()nen  mass  adheres  to 

354.  Calyx  and  corolla.  — The  leaves  of  ?^&?m.— Arur  lngie°rUt 
the  perianth  are  usually  arranged  upon  the  torus  in  two  or 
more  circles  or  in  a  low  spiral.  They  may  be  all  alike  or 
differentiated  into  two  series,  an  outer  and  an  inner.  In  the 
latter  case  those  of  the  outer  row  or  rows  constitute  the  calyx, 
and  the  inner  set  the  corolla. 

355.  The  calyx. — The  calyx  leaves,  or  sepals,  are  generally 
green  and  possess  a  great  variety  of  form.  When  separate, 
the  sepals  are  usually  sessile  and  broad,  with  more  or  less 
pointed  apex.  The  sepals  are  often  apparently  united  in  the 
manner  already  described  for  the  stamens,  the  originally 
separate  portions  appearing  as  teeth  or  lobes  at  the  rim  of  a 
cup  or  tube,  or  some  similar  structure.  Occasionally  the 
sepals  are  not  persistent,  but  tall  as  the  bud  opens  or  shortly 
thereafter.  More  commonly,  however,  the  calyx,  especially 
when  undivided,  remains  throughout  the  entire  development 
of  the  flower,  and  often  of  the  fruit. 

356.  The  corolla. — The  inner  set  of  perianth  leaves,  the 
petals,  constitutes  the  corolla.  The  corolla  presents  a  greater 
variety  of  form  and  color  than  does  the  calyx.  The  petals 
may  be  sessile  or  have  a  short  or  long  stalk  (fig.  274).  The 
corolla  ma)  develop  a  cup  or  tube,  as  described  tor  the  calyx, 
with  teeth  or  lobes  representing  the  petals  (c,  c,  fig.  267).     It 


'54 


PLANT  LIFE. 


may  be  lifted  on  a  common  tube  with  the  calyx  from  which 
it  then  seems  to  arise  ;  or  it  may  be  raised 
with  the  stamens,  which  then  seem  to  be 
attached  to  it,  as  in  figure  267  ;  or  stamens, 
corolla,  and  calyx  may  be  lifted  together 
(figs.  288,  355).  The  corolla  is  ordinarily 
not  persistent,  usually  falling  or  withering 
shortly  after  the  microspores  have  been 
lodged  upon  the  stigma. 

357.   Irregularity.  —  Both    corolla   and 
ig.  274.— Outline  of  a  calyx  are  often  radiallv  symmetrical — i.  e., 

petal    of    Lychnis, 

showing    long    stalk  the    parts    surrounding   the    center    of  the 

and  an  outgrowth,   n,  1 

the  Hguie.    Compare  stem    are    of   equal    size   and    like    shape, 

fjpr     rM  Aftpr    T  .nprQ- 

scn 


37. — After  Luers- 


md  may  be  divided  into  several  like  halves 
by  radial  planes  (figs.  275,  276).  But  often  the  symmetry 
of  the  calyx,  and  still  more   frequently  that  of  the  corolla, 


Fig.  275. 


Fig  276. 


Fir..  275. — A  flower  of  the  flax,  halved  ;  showing  radial  symmetry.  See  fig.  276.  Magni- 
fied 2  diam— After  liessey. 

FlG.  2-(k — Diagram  showing  the  arrangement  of  the  parts  of  a  flower  of  flax.  Outer 
circle,  5  sepals  ;  second,  5  petals;  third,  5  stamens;  fourth,  5  carpels,  each  divided  by  a 
false  partition  into  2  chambers.  Five  different  radial  planes  will,  therefore,  divide  this 
flower  into  halves.— After  Bessey. 


is  so  altered  by  unequal  growth  of  the  parts  that  the  flower 
can  be  divided  into  like  halves  by  only  one,  or  at  most  two, 


VEGE  TA  TI I  rE    KEPKOD  UCTION. 


255 


planes;  or  it  may  even  be  entirely  unsymmetrical.  This 
unlikeness  in  the  size  and  shape  of  the  accessory  leaves  not 
infrequently  extends  to  the  sporophylls  (figs.   277,  278). 

The  irregular  form  and  color  of  the  perianth  (when  other 
than  green),  including  the  variegation  of  the  ground  color 
by  lines  and  spots,  seem  to  be  dependent  upon  the  relation  of 
the  flower  to  insects.      (See  further  ^[  484. ) 


Fig.  277. — An  unopened  Sower  of  tlie  sweet  pea,  halved ;  showing  bilateral  symmetry 

(irregularity.     Slightly  enlarged.— After  Hessey. 
FlG.  278.  — Diagram  showing  the  arrangement  of  the  parts  of  the  flower  of  sweet  pea. 

Outer  circle,  calyx  >5-lobed>  ;  second,  5  petals,  the  two  lower  united;  third,  10  stamens, 

9  united  by  filaments,  1  separate  ;  center,  one  carpel.     Only  one  plane  will  divide  this 

flower  into  halves. — After  l'.essey. 

358.  Pollination. — Since  the  megaspore  is  enclosed  per- 
manently by  the  ovule,  and  in  angiosperms  the  ovules  are 
again  enclosed  by  the  pistil,  it  is  necessary  that  the  male  plant 
growing  from  the  pollen  spores  be  developed  in  the  neighbor- 
hood of  the  ovule  whose  megaspore  produces  a  female  plant. 
(See  ^jl"  341,  3S6.)  To  insure  this  a  portion  of  the  pistil 
forms  a  receptive  surface,  the  stigma,  upon  which  the  pollen 
spores  may  be  readily  lodged.  It  is  advantageous,  also,  to 
have  the  pollen  spores  of  one  flower  lodged  upon  the  stigma 
in  another  flower  of  the  same  sort  rather  than  upon  the 
stigma  of  the  same  flower.  The  process  of  lodgment  of 
pollen  on  a  stigma  is  (ailed  pollination.  If  the  pollen  from 
one  flower  is  tarried  to  the  pistil  of  another,  it  is  tailed 
cross-pollination. *      To    secure    pollination,     and    espei  iallv 

*  Since  fertilization  of  the  egg  i-  tin-  ultimate  object  of  pollination  and 


256 


FLA. XT  LIFE. 


cross-pollination,  the  agency  of  wind  or  water  or  insects  is 

employed.  To  the  peculiarities  of  these  various  agents, 
flowers  adapt  themselves  in  character  of  pollen,  color,  nectar, 
odor,  form  of  parts,  time  of  development  of  stamens  and 
stigma,  etc.  For  an  account  of  these  see  €  •  477-482. 
359.  Bracts. — In  the  immediate  neighborhood  of  the 
perianth  the  leaves  are  usually  modi- 
fied at  least  in  form  and  size,  and 
not  infrequently  in  color.  The 
leaves  in  whose  axils  the  flowers 
arise  are  called  bracts,  as  are  also 
those  which  subtend  branches  of  the 
inflorescence  (//',  //",  //3,  fig.  139). 
The  axis  of  the  flower,  when 
elongated  beneath  it,  usually  bears 
one  or  more  bractlets. 

The  bract  is  sometimes  large  and 
surrounds  the  entire  inflorescence, 
as  in  Indian  turnip  (fig.  279)  and 
the  calla,  when  it  may  be  vari- 
ously colored.  Highly  colored 
bracts    occur    in    the    scarlet     sage 

Fig.  279.— Inflorescence  of  Indian   and,       with       incOHSpicUOUS       flowers, 
turnip   (.1    s/uuiia),    surrounded 

by  a  large  striped  and  mottled  in     poinsettia     and     painted     cup, 

bract,  the  spatke.    Natural  size. 

—After Gray.  while  the  four  large  whitish    bracts 

of  dogwood  are  the  only  conspicuous  part  of  the  inflores- 
cence (fig.  280). 

Bracts  are  aggregated  to  form  an  involucre  beneath  a  head 
(T  104),  as  in  the  sunflower  family  (figs.  2S1,  409),  or  an 
umbel  (^[  104),  as  in  the  parsnip.  The  perianth  may  be 
almost  or  quite  wanting,  and  the  bracts  and  bractlets  may 
be  the  only  protective  leaves  for  the  sporophylls,  as  in  the 

generally   its   final   result,  the   terms  close-  or  self-fertilization   and   cross- 
fertilization  were  formerly  used.     The  word  pollination  is  preferable. 


VEGETATIVE   REPRODUCTION.  2$y 


Fig.  280. — Inflorescence  of  the  dogwood  (Cor nits  florida\  showing  four  white  bracts 
below- it,  giving  the  whole  cluster  the  aspect  of  a  single  (lower.  Two  thirds  natural 
size.— After  Baillon. 


Fig.  281.— Inflorescence  oi  yarrow  {Achillea  millefolium).  A,  seen  from  above;  /■', 
in  longitudinal  Bection.  r,  bracts,  forming  the  involucre  ;  d,  bra<  1-  in  whose  axils  the 
flowers  stand;  ra,  the  ray  flowers;  »//,  the  disk  flowers;  ..  corolla;  '.ovulary;  1, 
stigmas;  >,  the  common  torus.    A  magnified  about  8  diam. ;  B,  about  15  diam      Vftei 


258 


PLANT  LIFE. 


grasses  (fig.  282).  Bracelets  sometimes  form  a  sort  of  second 
calyx  beneath  the  true  calyx,  as  in  hollyhock.  In  the  straw- 
berry and  its  kin,  the  somewhat  similar  extra  whorl  of  leaves 


Fig.  282. 


Fig.  283. 


Fig.  284. 


Fig.  282. — A  single  flower  of  wheat,  showing  two  chaffy  bracts,  />,  v,  which  protect  it. 
For  the  parts  of  the  flower  see  fig.  2S3.     Magnified  about  5  diam. — After  Luerssen. 

Fig.  283. — The  flower  of  wheat  with  bracts  removed,  showing  two  fleshy  bractlets,  c,  c, 
the  lodicules,  which  at  time  of  blossoming  swell  and  open  the  bracts.  Three  stamens, 
and  a  carpel  with  two  styles  and  feathery  stigmas  constitute  the  flower  proper.  Magni- 
fied about  5  diam. — After  Luerssen. 

Fig.  284. — Outline  of  the  flower  of  strawberry,  seen  from  beneath,  c,  corolla  ;  k,  calyx; 
k',  epicalyx,  formed  by  the  union  of  the  stipules  of  the  sepals.  Slightly  reduced. — 
After  Luerssen. 


belongs  to  the  calyx,  being  the  stipules  of  the  calyx  leaves 
united  in  the  course  of  development  (fig.  284). 

The  "  cup  "  of  the  acorn,  the  "shuck  "  of  the  beechnut, 
and  the  "bur"  of  the  chestnut  represent  late-developed  out- 
growths beneath  the  flower  or  the  flower  cluster,  which  be- 
come scaly  or  spiny  as  the  nut  develops,  and  serve  to  protect 
the  forming  fruits. 

360.  The  torus. — In  the  vicinity  of  the  flower  leaves  the 
internodes  of  the  stem  are  rarely  developed,  so  that  the  nodes 
from  which  the  flower  leaves  arise  are  close  together.  More- 
over, the  axis  is  usually  enlarged,  so  as  to  give  greater  space 
for  the  numerous  leaves.  This  enlarged  portion  is  called  the 
receptacle  or  torus.  When  the  leaves  are  removed  or  fall 
naturally  the  torus  shows  ordinarily  a  rounded  or  conical  sur- 
face, with  close-set  scars  left  by  their  bases  (fig.  285).    When 


I  'EGE  TA  TI I  '£   REP  ROD  UCTION. 


259 


a  great  number  of  sporophylls  are  to  be  borne,  the  torus  is 
elongated,  as  in  the  mousetail  (fig.  286);  or  greatly  enlarged, 


Fig.  285.  Fig.  286. 

Fig.  2S5—  The  torus  of  a  flower  of  stonecrop  (Sedum  tematum),  with  the  leaves  re- 
moved to  show  scars  ;  two  leaves  of  each  kind  shown  a,  sepal ;  />,  petal ;  c,  stamen  ; 
ii,  carpel.     Magnified  several  diam. — After  Gray. 

Fig,  286.— Flower  of  mousetail  {Afyosurus  mittimus),  halved;  showing  s,  spurred 
sepal :  st,  stamen  ;  st' ,  a  staminode  or  sterile  stamen,  having  the  position  and  form  of 
a  petal ;  t,  elongated  torus  covered  with  carpels,  some  of  which  are  cut  through.  Mag- 
nified several  diam— After  Engler. 


FlG.  2S7.— Flower  of  the  strawberry,  halved;  showing  elongated  and  thickened  torus. 
Magnified  about  3  diam.-  After  Bessey, 


as  in  the  strawberry  (fig.   287);   or  transformed  into  ;i  cup,  as 
in  the  rose  (fig.  288). 

When  flowers  in  large  numbers  nre  very  closely  associated, 


!6o 


PLANT  LIFE. 


as  in  a  head  (•  104).  the  receptacles  arc  joined  to  form  a 
large  common  receptacle,  as  in  the  sunflower  and  its  allies 
(fig.  281).  The  receptacle  in  such  plants  may  he  a  cone, 
a  dome  (fig.  409),  or  a  more  or  less  flattened  disk.      In  the 


Fig.  288.  Fig.  289. 

Fig.  288. — Flower  of  sweetbrier  rose,  halved;  showing  urn-shaped  torus.    Compare  fig. 

139.     Natural  size. — Attn-  Bessey. 
I  ■  ,      Tin-    inflorescence  of  fig.  halved  lengthwise;  showing  common  torus   on 

whose  interior  surface  many  flowers  are  formed.  Two  fig  wasps  are  near  the  opening 
of  the  flower  chamber,  one  outside,  while  the  other  has  just  crawled  in  among  the 
flowers.     Natural  size. — After  Kerner. 

fig  the  common  receptacle  is  pear-shaped,  with  the  edges 
almost  meeting  above  and  the  flowers  distributed  over  the 
inner  face  of  the  fleshy  sac  (fig.   289). 


III.  Brood  buds,  etc. 

361.  Definition. — Single-celled  spores  pass  without  any 
sharp  distinction  into  the  multicellular  bodies  known  as  brood 
buds.  For  convenience,  however,  brood  buds  maybe  de- 
fined as  multicellular  (sometimes  unicellular)  bodies  capable 

of  producing  a  new  plant  of  the  same  phase  as  that  from 
which  they  arise.  Since  this  is  a  distinction  for  conve- 
nience merely,  it  is  not  desirable  to  distinguish  brood  buds 


VEGETATIVE   REPRODUCTION.  26l 

from  spores  until  the  mossworts  are  reached,  in  which  the 
alternation  of  phase  is  well  marked.  In  their  simplest  form 
such  buds  consist  of  a  single  cell,  though  more  commonly 
they  are  two-  to  several-celled.  Some  or  all  of  their  cells  are 
in  the  embryonic  stage  (^]  256).  Like  spores,  they  are  sup- 
plied with  reserve  food. 

362.  Simple  forms. — The  form  of  brood  buds  is  various. 
When  not  differentiated  into  distinct  organs,  they  are  club- 
shaped,  lenticular,  or  spherical.  In  some  thalloid  liverworts 
(Marchantia  and  Lunularid)  they  are  produced  on  the  surface 
of  the  thallus,  surrounded  wholly  or  on  one  side  by  an  out- 
growth from  the  surface  forming  a  cup  or  a  crescentic  ledge 
(figs.  59,  290,  291).      In  some  mosses  brood  buds  arise  from 


Fig.  290. — Thallus  of  Marchantia,  seen  from  above,  showing  the  cups  containing  brood 
buds.     See  fig.  291.     Natural  size. — Alter  Kerner. 


the  apex  of  the  stem,  either  in  cup-like  clusters  of  leaves  or 
exposed  (A,Af,  fig.  292);  in  others  they  are  smaller  and 
simpler  and  are  developed  upon  the  leaves  (B,  B\  fig.  292). 
In  all  the  mossworts  they  belong  to  the  gametophyte. 

363.  Shoots. — In  femwortS  and  seed  plants  the  brood  buds 
belong  to  the  sporophyte.  In  the  latter  they  are  espe<  iallj 
abundant,  and  often  reach  considerable  size  ami  complexity 
before  being  separated  from  the  parent,  usually  consisting  of 
a  short    axis  with  a  growing    point   and   at    least  rudimentary 


262 


PLANT  LIFE. 


91.  Fin.  2152. 

the  development  of  a  brood  bud  of  Marchantia  ; 


ill  seen  from 


Fig. 

Fig.  291. — Six  stages 
side.     I,  very  young 

older,  terminal  cell  divided  trans- 
versely. Ill,  IV,  V,  successively  older  stages.  VI.  mature,  cells  not  shown:  two 
growing  points  localized  on  right  and  left  edges.  I-V,  magnified  about  250  diam.; 
VI,  about  25  diam. — After  Sachs. 

Fig.  292. — Brood  buds  of  mosses.  A  ,  upper  part  of  the  stem  of  Aulacomnium  audio- 
gynu m .  with  a  cluster  of  brood  buds  at  apex  (magnified  about  8  diam.),  one  of  which  is 
enlarged  120  diam.  in  A',  />',  tip  of  leaf  of  Syrrkopodon  sender  (magnified  about  i" 
diam.)  showing  brood  buds  ;  />",  some  more  enlarged  labout  40  diam.).  — After  Kerner. 


Fig.  293. — Young  plants  developing  from  adventitious  buds  on  leaves  of  a  fern  (Aspic 
vhich  they  readily  separate  to  form 


muni  i>ulbi/,-r iiniK  from  ■ 
size.     />',  magnified  2  diam. 


plants.     A,  natural 


VEGETA  TIVE   RETROD  L'CTION. 


263 


leaves.      They  generally  arise  upon  the  stem,   more 

from   the  leaves  or  the    root.     Upon 

the  stem  they  usually  take  the  place  of 

shoots  of  other  forms,  developing  from 

axillary   buds    (figs.    294,    296).        If 

formed  on  leaf  or  root  it  is  always  from 

adventitious  buds  (fig.  293). 

Every  possible  gradation  exists,  from 
the  simplest  to  those  with  well-de- 
veloped members,  constituting  a  plant 
of  some  size.  They  may  be  artificially 
grouped  as  follows  : 

364.  {a)  Buds. — In  these  the  axis 
is  short  and  the  leaves  scale-like.  When 
most  highly  developed  the  quantity  of 
reserve  food  is  considerable  and  the 


rarely 


Fig.  294. — Fleshy  buds  in  axils 
of  the  leaves  of  a  lily  (I. ili- 
um bulbi/eruiti).  Some- 
what reduced.  —  After  Van 
Tieghem. 


.y^ 


v\/f 


t. 


3M  : 


jL_I- 


1 


Fig.  295.— Pond  weed  iPolamogeton  crispus).    Detachment  o)  spe<  i.il  shoots,  hibenuu  - 

ula,  which  are  to  hibernate  under  water.  The  plant  ./  has  one  oi  these  shoots  at  the 
tip;  B  lias  just  loosened  one,  /;,  which  is  sinking  to  the  bottom.  Two  thirds  natural 
size.— After  Kemer. 


264 


PLANT  LIFE. 


parts  of  the  bud  are  often  distorted 
by  the  enlargement  of  the  tissues 
to  contain  the  food.  The  fleshy 
buds  which  readily  separate  from 
the  axils  of  the  leaves  of  some 
garden  lilies  (fig.  294),  and  those 
which  replace  the  flowers  in  some 
cultivated  onions,  are  well  known. 
(Compare  also  fig.  106.) 

365.    (/')  Hibernacula. — Some- 
what similar  but  more  highly  de- 


Fig.  296.— A  plant  of  stonecrop  [Sedum  dasyfihyllum).  Offsets  are  produced  near  the 
base  on  short  brandies  o,  o ;  at  the  tip  of  longer  branches,  o' ;  and  in  place  of  the  flow- 
ers, o".     Natural  size.— After  Kerner. 


Fig.  297.— Formation  of  runners  in  the  strawberry.  ,t,  the  mother  plant ;  b,  voung  plant 
formed  at  tip  of  first  runner;  c,  plantlet  at  tip  of  second  ;  a  third  has  put  out  from  c. 
Slightly  reduced.— After  Seubert. 


VEGET.  I  I'l  I  E   RETROD  UCTION. 


265 


veloped  brood  buds  are  formed  at  the  approach  of  winter 
about  the  base  of  the  stem  in  many  perennials  with  her- 
baceous tops.  These  are  separated  by  the  death  of  the  parent 
stem  and  produce  new  plants 
in  the  spring.  Some  aquatics 
show  a  similar  habit,  dropping 
short  shoots  to  the  bottom  of 
the  water  in  autumn,  which 
are  to  grow  in  the  spring  (fig. 

295)- 

366.  (r)  Offsets,  etc. — 
Some  plants  produce  special 
branches,  either  underground 
or  aerial,  which  develop  at 
their  extremities  new  plants  or 
special  structures  for  their  for- 
mation. The  housedeek  or  live- 
forever  (fig.  369)  and  stonecrop 
(fig.  296)  reproduce  themselves 
by  offsets.  These  are  short 
branches  with  a  rosette  of 
leaves  at  the  tip  which  is  read- 
ily detached  and  rolls  away, 
to  take  root  at  the  first  oppor- 
tunity    and    establish    a    new 

plant.  The    Strawberry    and  Fig.  298.— A  plant  of  eel-grass  (Vallisne- 

ria  spiralis)  forming  new  plants,  a,  b,  at 

eel-gl'aSS  form  long  leafleSS  tips  of  runners,  arising  from  axils  of  lower 
leaves.      One   third   natural    size.      \tu-r 

branches  which  take  root  at  the     Schnizlein. 

tip  and  produce  new  plants,  the  slender  runner  subsequently 
perishing  (figs.  297.  298).  The  white  potato  forms  at  the 
end  of  slender  underground  branches  elongated  tubers  upon 
which  are  numerous  buds,  any  one  of  which,  nourished  by 
the  reserve  food  in  the  tuber,  may  produce  a  new  shoot. 
The    slender    stem    by    which    the    tuber    is   connected    with 


266 


PLANT   LIFE 


the  main  axis  perishes  at  the  end    of  the   growing    season 
(fig.  299). 

367.    (d)    Cuttings    or    scions.— Closely  related    to    this 
mode   of  reproduction   is   that  by    the   separation   of  fleshy 


Fig.  299. — A  seedling  potato  plant.  (  is  the  baseoi  the  stum,  below  whi<  h  is  the  primary 
root.  r.  The  primary  leaves  <  t,  are  still  present.  The  early  leaves,./!  rlre  not  so  much 
branched  as  later  ones  will  In-.  In  the  axils  of  the  lower  leaves  arise  the  branchi 
with  scale  leaves,  e'e,  and  secondary  roots,  1  .  The  tips  of  these  branches,  when 
illuminated,  bear  foliage  leaves,  /' ;  but  usually  they  thicken  into  tubers,//.,  which 
have  scale  leaves,  e'i   ,  in  whose  axil    bud  an    formed,  the     o-called  "  eyes "  of 

the  tul  hi       Natural  size. — After  Duchartre. 

members,  upon  which  are  subsequently  developed  adventi- 
tious buds,  which  give  rise  to  new  plants.  The  thick  leaves 
of  Bryophyllum  are  often  Mown  off  by  storms,  and  produce 

new  plants   from   buds  formed  at   the   teeth  along  the  edge. 


I  'EGE  TA  Tl  I  £   RETROD  UCTION. 


267 


Some  species  of  Kleinia,  natives  of  Cape  Colony,  have  fleshy 
Stems,  jointed  at  intervals,  so  that  they  easily  break  there. 
When  broken  off  by  an  accident,  the  piece  rolls  away,  takes 
root  from  the  under  side,  and  sends  up  shoots  from  the  upper. 

Advantage  is  taken  of  this  power  of  severed  parts  to  form 
adventitious  roots  and  shoots  in  the  artificial  propagation  of 
domestic  plants.  Suitable  portions  of  shoots  or  leaves  for 
the  development  of  new  plants  under  proper  conditions  are 
called  cuttings,  scions,  or  "buds."  They  may  generally  be 
grown  in  water  or  soil  ;  or  they  may  be  securely  fastened  in 
a  slit  or  wound  in  another  plant.  The  latter  process  is 
known  as  grafting  or  budding,  according  to  the  form  of  the 
implanted  part.  Indeed  brood  buds  in  general  may  be 
looked  upon  as  natural  cuttings  or  scions. 

368.   Branching. — A   further  modification  of  this  method 
of   reproduction    is    to    be 
served    in     the     formation 
new    individuals    through   pro- 
gressive    death     of     the     older 
parts.      If  a  plant,  dying  thus, 
be  a   branching   one,  death  will 
sever  the  branches  as  it  reaches 
them      sooner     or     later,      and 
each  branch  then   becomes  an 
independent     plant.        This      is 
seen     in     its    simplest    form    in 
those   plants  which  have  a  hori- 
zontal  branching   thallus  whose  p 
base  dies  as  the  apex  elongates  Fig.  300.— Outline  of  a  thaiius  of  u„>- 

\  1        •  •  chant ia  geminata.      The   base    D  is 

(fig.     300).         It     IS    common     in      dying  as  the   apices  are  growing  and 

branching.  Wheti  death  reaches  the 
plants  with    underground  Creep-      first  fork  there  will  be  two  independent 

plants;  at  the  second  there  will  be  four, 

mg* stems  which  send  up  aerial    andsoon. 

leaves  or  shoots  annually,  as  do  the  ferns  of  temperate  regions 

and  main  glasses  and  mints. 


CHAPTER  XVIII. 

SEXUAL  REPRODUCTION. 

369.  Cell  union. — All  methods  of  sexual  reproduction 
consist  in  the  formation  of  a  single  cell  by  the  union  of  two 
specialized  cells,  known,  respectively,  as  the  male  gamete  and 
the  female  gamete.  The  essential  step  in  their  union  is  the 
coalescence  of  the  nuclei.  The  cell  thus  formed  is  capable 
of  developing  into  a  new  plant  under  suitable  conditions, 
and  is,  consequently,  a  spore.  Such  sexually  produced  spores 
must  not  be  confounded  with  non-sexual  spores  (see  ^[  304). 

370.  Origin. — It  is  scarcely  to  be  doubted  that  the  earliest 
methods  of  reproduction  were  vegetative,  and  that  sexuality 
has  been  acquired  by  a  gradual  modification  of  cells  previ- 
ously devoted  wholly  to  ordinary  processes  of  growth.  The 
probable  history  of  the  origin  of  sexual  cells  and  sex  organs 
can  onlv  be  inferred  from  the  fact  that  the  simplest  plants 
show  no  sexuality,  others  show  imperfect  sexuality,  and  still 
others  complete  sexuality.  The  data  are  very  imperfect,  but 
they  enable  us  to  form  at  least  an  intelligent  idea  of  how 
sexuality  may  have  been  acquired. 


Theory  of  sexuality. 

371.  Rejuvenescence. — Among  the  processes  of  growth 
in  the  simpler  plants,  especially  the  fission-algne  (^[  11),  one 
of  the  most  striking  is  that  known  as  rejuvenescence.  In  this 
process  the  protoplasm  of  the  cell  escapes  from  the  cell-wall, 
and  acquires  special  motor  organs  known  as  cilia,  which  en- 

268 


SEXUAL   REPRODUCTION.  269 

able  it  to  swim  rapidly,  but  apparently  aimlessly,  through  the 
water.  In  this  form  it  is  essentially  a  zoospore.  (See  ^  306.) 
After  having  moved  about  for  a  variable  time  and  perhaps 
increased  its  volume  by  growth,  it  loses  its  cilia,  surrounds 
itself  again  with  a  cell-wall,  and  resumes  its  ordinary  mode  of 
life.  In  filaments  of  some  multicellular  algae  a  similar  process 
occurs.  The  contents  of  any  cell  may  escape  by  the  solution 
of  the  cell-wall  and  become  a  zoospore.  After  swimming 
about  for  a  time  the  zoospore  may  come  to  rest,  secrete  a 
cell-wall,  and  by  repeated  divisions  in  one  plane  produce  an 
individual  similar  to  the  parent.  (See  ^|  24.)  It  is  evident 
that  such  a  method  would  give  rise  economically  to  a  con- 
siderable number  of  individuals.  The  process  is  essentially 
the  separation  of  the  filament  into  pieces,  each  being  the 
contents  of  a  single  cell. 

372.  Conjugation. — In  other  filamentous  algae  the  cell- 
contents,  instead  of  escaping  as  a  single  zoospore,  divide  into 
two  or  more  zoospores.  If,  while  these  are  still  active,  two 
accidentally  collide,  the  possibility  of  their  adherence  and 
and  the  fusion  of  the  two  into  one  is  conceivable.  Such 
fusion  actually  occurs  among  the  zoospores  of  alga;,  and  is 
(ailed  conjugation,  but  in  observed  cases  it  follows  a  definite 
method,  and  is  not  merely  accidental.  It  is  probable,  how- 
ever, that  the  first  occurrence  of  conjugation  was  accidental, 
and  that  it  has  become  fixed  and  definite  because  those  indi- 
viduals in  which  it  occurred  with  most  certainty  and  regular- 
ity thereby  produced  the  most  vigorous  offspring. 

373.  Imperfect  sexuality.  —  In  the  alga  Ulothrix,  we  have 
a  plant  in  which  many  of  the  processes  just  described  still 
occur.  It  produces  zoospores  of  two  kinds:  (1)  large  ones, 
with  four  cilia  (C,  fig.  301),  formed  in  pairs  in  each  cell  (B)  ; 
(2)  small  ones,  having  two  (rarely  four)  cilia,  and  arising 
eight  or  sixteen  from  each  mother  cell  (D).  Both  these  sorts 
of  zoospores  will  grow,  after  a  period  of  swimming,  into  new 


270 


PLANT   LIFE. 


plants,  though  the  small  ones  produce  very  slender,  weak  fila- 
ments (fig.  302).  Beside  the  zoospores,  Ulothrix  produces, 
under  certain   conditions,   gametes,  which   are   precisely  like 


Fir,.  301. —  Ulothrix  zonata.  .1,  a  young  filament  with  rhizoid  cell,  r,  at  base.  B,  bit 
of  a  filament  from  whose  cells  large  zoospores  are  escaping  through  a  pore  in  the  side- 
wall.  C,  a  single  large  zoospore.  D,  bit  of  a  filament  from  whose  cells  small  zoo- 
spores lor  gametes1  are  esi  aping  / ■',  small  zoospores  lor  gametes  .  /•',  gametes  con- 
jugating, (r,  same,  conjugation  complete.  //.  zygote,  before  formation  of  wall  to 
become  a  resting  spore.     Magnified  4S2  diam. — After  Dodel-Port. 

the  small  zoospores  in  appearance.  But  their  behavior  is 
different.  They  usually  conjugate  freely  in  pairs  and  produce 
resting  spores.      If,   however,    they  do  not  conjugate,   each 


SEXUAL   REPRODUCTION. 


27I 


may  round  itself  off  and,  alone,  become  a  resting  spore. 
These  resting  spores,  after  a  dormant  period,  germinate  and 
develop  into  new  plants. 

In  llothrix,  therefore,  the  gametes  are  imperfectly  sexual. 
Failing  to  conjugate,  as  many  do,  they  may  still  develop  into 
new  individuals.  A  con- 
sideration of  the  appearance 
and  behavior  of  the  gametes 
leaves  little  doubt  that  they 
are  merely  small  zoospores 
which  have  acquired  imper- 
fectly the  habit  of  conjuga- 
tion and  retained  partially 
the  power  of  independent 
growth. 

374.  Further  develop- 
ment.— -The  perfecting  of 
reproductive  methods  fol- 
lowed the  two  lines  just  sug- 
gested. On  the  one  hand, 
complete    sexuality  was   ac- 

Fir..  302.— Sporelings  of  Ulothrix  zon.it*. 
quired  by  certain  Cells,  while      a,    a   young  plant    from   a   large   zoospore. 

/>,  young  plants  from  small  zoospores  which 
Others  Were  more   Completely       germinated  without  leaving  the   mother  cell. 

Magnified  4S2  diam.— After  Dodel-Port. 

specialized  as  non-sexual  re- 
productive bodies.      The  latter  have  already  been  discussed 

(T3°4ff-)- 

Tracing  now  only  the  line  of  sexual  development,  it  is 
probable  that  the  first  step  in  this  differentiation  was  the 
failure  of  some  of  the  zoospores  to  escape  from  the  cell  pro- 
ducing them.  From  this  point  two  lines  of  development 
diverge. 

375.  1.  Isogamy. — Along  one  of  these  lines,  the  zoo- 
spores ceased  to  form  cilia,  and  became  non  motile  sex 
cells,  in  some  cases  similar  in  form  and  function,  and  in  others 


272 


PLANT   LIFE 


like 


in  form  but  unlike  in  behavior.  This  leads  to  the  com- 
pletest  form  of  conjugation,  as  seen 
in  Mesocarpus,  Spirogyra,  and  other 
Conjugate.  (See  *[  25.)  In  these 
the  contents  of  one  cell  of  a  filament 
enter  those  of  another  either  by  a 
partial  solution  of  the  partition-wall 
between  them  or  by  the  formation  of 
a  tube-like  outgrowth  from  one  or 
both  of  the  cells  concerned,  so  that 
when  these  tubes  come  in  contact  and 
have  their  ends  absorbed  the  contents 
of  one  cell  passes  over  into  that  of 
the  other  (fig.  303).  The  cells  con- 
jugating in  this  way  may  he  either 
neighboring  cells  of  the  same  fila- 
ment or  cells  of  different  filaments 
brought  into  proximity  by  acccident. 

Fig.  303  —Conjugation  of  .S> iro-  , 

gymquinina.  The  cells  a,  a'  In  the  course   of  development  in  this 

are  just  forming  the  conjugat-  .  .  ,  . 

ing  tube;  the  contents  not  yet  direction        conjugation         reaches        its 
fully  reorganized   as  gametes.  _  i        ■   i 

The  body  protoplasm  is  not  highest  perfection,  being  secured  with 

shown     in     these     two     cells,  ...  .  ,        . 

though  it  is  in  the  others  such  certainty  that  non-sexual  methods 

(compare   fig.   25,    of   another  . 

species  of  Spirogyra).     The  are  almost  entirelv  abandoned. 

cells  b,  b'  have  completed  the         «.„„_,,  „, 

tube ;  the  ends  have  been  dis-      376.   2.  Heterogamy. —  i  he  second 

solved  and   the   contents   of  b 

is  passing  over  into  b' .     This  ljne    of   development    Was  followed    In- 
process  is  nearly  completed  in 

cells  c,  c'.   2,  2,  zygotes,  with  other  algae,  and  the  method  proved  so 

protecting  wall,    thereby    pre-  ...  ,  - 

paredto  become  resting  spores,  efficient  that  it  became  the  dominant 

Magnified    150    diam.  —  After 

Strasburger.  one    in  the  plant  kingdom.      Among 

these  algre  there  occurred  a  differentiation  of  the  zoospores. 
The  first  step  in  this  differentiation  was  an  increase  in  size 
of  one  of  the  sex  cells,  so  that  they  differed  both  in  action 
and  in  form.  To  distinguish  one  from  the  other  the  larger 
sex  cell  is  called  the  female  cell,  or  egg,  and  the  smaller,  the 
male  cell,  or  sperm.      A  further  difference  arose  in  the  com- 


SEXUAL   REPRODUCTION. 


273 


plete  loss  of  motility  by  the  female  cell  (fig.  304).  When 
these  differences  exist  in  the  sex  cells  their  union  is  no 
longer  called  conjugation,  but  fertilization,  the  active  male 
cell  being  said  to  fertilize  the  quiescent  female  (  ell. 

377.   Sex  organs. — A  further  stage  in  the  development  of 
sexuality  is  reached  when  the  cells  producing  the  sperms  or 


Fig 
carpus.     /■.  sperm 


Differentiation  of  gametes  in  some  marine  algae 
lost 

1.  ./.  1 
the  extreme  "I  difference  in  she  in  gametes.    All  magnified  equally  (about  700  diam.), 


egg  of  Za 

before  fertilization  which  is  about  to  occur  in  (/ 


ke  gametes  of   Keto- 
ne egg  loses  its  cilia  and  rounds  itself 
.  sperm,  _/.  egg  of  incus.    This  is 


the  eggs  are  differentiated.  The  cell  or  the  Organ  producing 
the  egg  has  been  known  by  various  names  in  different  groups 
of  plants.  An  appropriate  general  name  for  it,  without  refer- 
ence  to   its   structure,    is    the    ovary.      (See    further*    335.) 


274  PLANT  LIFE. 

The  male  organ  was  called  the  antheridium,  from  the  idea 
that  it  was  like  the  anther  of  seed-plants,  which  was  once 
supposed  to  be  the  male  organ  of  the  flower.  There  is  no 
special  objection  to  the  name,  but  a  more  appropriate  one  for 
it  is  the  spermary,  since  these  male  cells  are  known  as  the 
spermatozoids  or,  briefly,  the  sperms. 

The  final  step  in  the  development  of  sexuality  is  the  restric- 
tion of  the  formation  of  sex  organs  to  a  certain  phase  in  the 
life  history  of  the  plant,  which  is  therefore  known  as  the 
sexual  phase,  or  gametophyte,  the  remaining  phase  or  phases 
being  called,  for  the  sake  of  distinction,  non-sexual,  and  con- 
stituting the  sporophyte.  The  gametophyte  alternates  with 
the  sporophyte,  giving  rise  to  the  phenomenon  known  as  the 
"alternation  of  generations."      (See  %  55.) 

378.  Directive  agents. — To  secure  the  union  of  the  male 
and  female  cells,  the  male  gamete  must  be  directed  to  the 
female.  By  what  means  this  is  accomplished  is  not  fully 
known.  Organic  acids  and  sugar  exercise  such  an  influence 
on  certain  sperms  that  they  swim  towards  the  source  of  these 
substances.  The  wide  distribution  of  such  compounds  sug- 
gests that  probably  their  presence  in  the  female  gamete  may 
render  it  attractive.  W  this  is  true,  the  sperms  exhibit  a  spe- 
cial irritability  towards  these  materials,  whose  diffusion  acts 
as  a  stimulus. 

Isogamy. 

Sexual  reproduction,  as  developed  among  existing  plants, 
shows  two  main  types,  known  as  isogamy  and  heterogamy. 

379.  Isogamy  is  thai  mode  of  sexual  union  in  which  the 
size  and  form  of  the  gametes  is  alike.  In  some  cases  the 
behavior  also  of  both  male  and  female  isalike,  while  in  others 
the  male  shows  a  greater  power  of  movement.  When  both 
are  equally  motile  and  escape  from  the  cell,  conjugation  occurs 
wherever  they  happen  to  come  in  contact.     The  form  is  usually 


SEX  i  A  L    KEF  ROD  UCTION. 


?75 


pear-like  {E,  fig.  301).  The  protoplasm  at  the  narrower  end 
is  more  transparent  and  hears  two  or  more 
cilia  ;  while  the  larger  end  is  occupied  hy 
the  reserve  food  and  particularly  the  chloro- 
plasts,  if  present.  Union  of  free  motile 
gametes  occurs  by  gradual  coalescence,  be- 
ginning at  the  pointed,  transparent  end  {F, 
fig.  301).  When  the  conjugation  is  com- 
plete the  resulting  spore  (zygote)  usually 
acquires  a  spherical  form,  soon  secretes  about 
itself  a  wall,  and  either  begins  to  grow  at 
once  into  a  new  plant  or  thickens  the  wall 
and  becomes  dormant  for  a  time  as  a  resting 
spore.  In  other  cases  the  form  of  the 
gametes  is  determined  only  by  the  shape  of 
the  cell,  from  which  they  do  not  escape.  The 
entire  cell  contents  constitutes  the  gamete 
(figs.  303,  304).  In  such  plants  both 
gametes  may  be  equally  motile  and  meet 
in  a  branch,  the  conjugating  tube,  to  form  a 
spore,  as  in  Mesocarpus  (fig.  304)  ;  or  the 
male  gamete  may  be  motile  and  migrate  from  the  cell  in 
which  it  is  produced,  through  the  conjugating  tube  into  the 
cell  containing  the  female  gamete,  with  which  it  fuses,  as  in 
Spirogyra  (l^.  303). 

The  spore  thus  formed  may  be  a  resting  spore,  in  which 
case  it  secretes  about  itself  a  thick  wall,  and  remains  dormant 
for  several  weeks  or  months.  In  the  plants  just  referred  to, 
the  spores,  funned  in  early  summer,  with  the  remnants  of  the 
parent  cell-walls  about  them,  sink  to  the  bottom  of  the  water, 
and  do  not  germinate  till  the  next  spring. 


Fig.  305. — Conjugation 
of  Mesocarpus.  The 
contents  of  the  two 
upper  cells  are  accu- 
mulating in  the  con- 
jugating tube  to  form 
a  zygote,  which  is 
complete  in  the 
lower  tube.  Magni- 
fied about  150  diam. 
— After  DeHary. 


276 


FLAX  J-   LIFE. 


Heterogamy. 

Heterogamy  is  that  mode  of  sexual  union  in  which  the  sex 
cells  are  unlike,  being  differentiated  into  sperms  and  eggs. 

380.  The  sperms. — The  body  of  the  sperm  is  the  cell 
nucleus,  surrounded  by  a  small  amount  of  protoplasm  which  is 
often  extended  into  one  or  more  cilia  (fig.  306).  The  more 
complete  the  differentiation  of  the  sperm  the  smaller,  as  a 
rule,  is  the  amount  of  body  protoplasm.  Whether  or  not  the 
sperm  is  motile  depends  upon  the  conditions  to  which  it  has 
become  adapted.  Whenever  motile,  fertilization  must  occur 
in  the  presence  of  water  of  amount  sufficient  to  permit  the 
sperm  to  swim  to  the  egg. 


Fig.  306. — Sperms  of  various  plants,  showing  variety  of  form,     t,  Volvox  aureus; 
1,  Vaucheria  synandra  .   ;,  Ckarafragilis ;  4,  Fucus  serratus ;  5,  Marchantia 
7,    Marsilia   vestita.      Magnified   kk»i 


polymorpha  :  6,    Equisetum    Telmatei 
diam.  — After  Mbbius 


The  spermary  may  produce  only  one  sperm  (fig.  307),  or 
its  contents  may  divide  into  many  (fig.  310).      When  single, 


SEX  I  A  1    REPROD  UCT10N 


2/7 


the  form  of  the  sperm  is  usually  that  of  the  cell  in  which  it 
is  produced.  U  it  is  set  free,  it  may  become  globular,  and 
have  slow  amoeboid  movements,  or  it  may  be  entirely  im- 
motile.  In  the  latter  case  it  must  depend  upon  the  move- 
ments of  the  water  into  which  it  escapes  for  transference  to 
the  vicinity  of  the  egg.  The  sperm  may  be  ovoid  and  fur- 
nished at  the  end  with  one  or  more  cilia ;  or  elongated  and 
bent  or  coiled  one  or  more  times.  The  elongated  forms 
have  almost  invariably  two  to  many  cilia  (fig.  306). 

381.  The  spermary. — The  organ  in  which  the  sperms  are 
produced  is  the  spermary  or  antheridium.  It  is  either  simple 
or  compound.  A  simple  spermary  consists  of  a  single  cell 
whose  contents  is  transformed  into  one  or  more  sperms. 
Simple  spermaries  occur  only  in  algae  and  fungi,  and  by 
reduction  among  seed- plants.  (See  ^[ 
3S5.)  If  more  than  one  sperm  is  to  be 
formed,  the  nucleus,  originally  single, 
becomes  divided  into  as  many  parts  as 
there  are  to  be  sperms  (sometimes  into 
more  than  become  mature).  The  total 
number  of  sperms  produced  by  a  plant  is 
related  somewhat  to  the  number  of  eggs, 
but  particularly  to  the  chances  of  the 
sperms  reaching  the  egg. 

If  there    is   but  a 


Fig.  307.-  The  sex  organs 

ingle  sperm  iormeu    of    Peronospora.     /;, 

'  hvplia  which  has  devel- 

bv  each  spermary,   either  the  number  ot    oped  at  the  end   the 

spermaries    is    great    or   some    adaptation 

exists  for  the  certain  transfer  of  the  sperm 

to    the   e^g.       In   Cystopus    and   its   allies, 

for   instance,    a   branch    of  the   spermary 

grows   into    the   ovary,  through  which    the 

sperm  passes  to  the  egg  (fig.  307). 

A    simple   spermary  arises  either   by  the 


egg  (the  centra] 
dark  sphere  <'.■'.  hypha 
which  lias  developed  the 

spermary.  >:.  who 
toplasm,  constituting    .1 
single  sperm,  is   passing 
through    the    fertilizing 
tube  (a  branch    ol    the 

Magnified    $50    diam 
Aftei  DeBary. 

differentiation    of 


one  of  the  ordinary  cells,  or  of  a  special  lateral  branch,  as  in 


2  78 


PLANT   LIFE. 


the   filamentous   algae   and  fungi   (figs.   307,   308).      In   the 
thallus  of  multicellular  algas  it  may  be  the  terminal  cell  of  a 


a       A 


Fig.  308. — Sex  organs  of  water  flannel  {I'aucheria  sessilis).  A,  a  portion  of  filament 
with  two  lateral  branches,  a,  Ag.  In  a  the  spermary  has  already  heen  divided  from 
the  body  cavity  by  a  partition  wall.  In  r'x ,  a  partition  will  form  at  juncture  with  main 
axis  (see  fig.  /■).  when  .  ,  becomes  the  ovary.  B,  the  ovary,  mature,  having  opened 
and  extruded  .v/,  a  portion  of  the  protoplasm..  What  remains  is  the  egg.  The  chloro- 
plasts  have  accumulated,  leaving  a  clear  receptive  spot  opposite  entrance  of  ovary.  (  , 
sperms,  which  escape  at  maturity  from  A,  <i.  D,  ovary  with  egg  about  to  be  fertil- 
ized; the  sperms  have  collected  at  the  opening.  A,  />',  /»,  magnified  about  ioodiam. 
C,  magnified  much  more  (about  350  diam.?).  A,  />,  after  Sachs;  />',  C,  after  Prings- 
heim. 

branch  or,  in  the  leaf-like  forms,  a  cluster  of  surface  cells. 
In  Fucus  the  spermaries  (figs.  309,  310)  are  terminal  cells 
of  much-branched  hairs  which  J 

develop   from   the  surface  cells 
of  a  narrow-mouthed   pit  like 


Fig.  309.— A  portion  of  a  branched  hair  from  a  conceptacle  of  bladder  wrack  (/■:,,  us 
vesicutosus).  The  darker  cells  are  the  spermaries.  Magnified  160  diam. — After 
Thuret. 

Fig.  310. — Spermaries  of  Fucus  vesiculosus,  showing  the  escape  of  the  sperms.  Magni- 
fied 350  diam. — After  Thuret. 


SEX  UA  L    RE  PROD  UCTIOX, 


279 


that  for  the  ovaries  (fig,  326).  (See  also  fig.  42.)  The 
sperms  are  set  free  by  the  rupture  of  the  wall  of  the  spermary. 
382.  A  compound  spermary  consists  of  one  or  more  cells 
in  which  the  sperms  are  to  be  produced  (each  correspond  in- 
to a  simple  spermary),  surrounded  by  a  wall  formed  of  a 
single  layer  of  cells  (rarely  more).  Compound  spermaries 
are  found  only  in  Characese,  mossworts,  and  higher  plants. 
The  spermary  is  a  spherical  or  elongated  sac,  raised  upon  a 
stalk,  or  sessile  ;  free  upon  the  surface  of  the  plant,  or  sunk 
in  a  pit  (fig.  311).     The  cell  in  which  each  sperm  is  formed 


Fig. 


longitudinal  section   ot  a   male  head  of   Marchantia.     t,  portion  of 


thallus  ;  ha,  enlarged  head  or  receptacle;  a,  spermaries,  sunk  in  pits  opening  at  0. 
Magnified  about  15  diam.  />',  compound  spermary.  a/,  its  wall,  surrounding  the 
immense  number  oi  minute  regularly  arranged  sperm  mother  cells;  st,  its  stalk. 
Magnified  about  &  1  diam.  —After  Sai  hs. 


is  called  a  "sperm  mother  cell."  Each  contains  a  single 
nucleus  which  enlarges  to  form  the  sperm  of  that  cell  (fig. 
312).  The  sperms  arc  set  free  by  the  breaking  down  of  the 
walls  of  the  mother  cells  at  about  the  same  time  that  the 
outer  wall  of  the  spermary  is  ruptured  by  the  destruction  of 
one  or  more  of  its  cells. 

The  form  of  the  vegetative  body  of  the  gametophyte  in  all 


2  SO 


PLANT  LIFE. 


but  the  seed  plants  was  described  in   Part  I.       The   forms   of 
the  spermaries  are  as  follows: 

383.  Chara. —  The  compound  spermary  of  Chara  (fig. 
313)  consists  of  a  spheri<  al  case  composed  of  four  triangular, 
plate-like  cells;  from  the  inner  face  of  each  projects  a 
handle-like  cell  to  whose  end  are  attached  24  filaments,  each 
composed  of  100-200  disk-shaped  cells.      Each  of  these  con- 


Fig.  312. — Development  of  a  sperm  of  a  liverwort  I  Pellia  epiphylla\.  n,  mother  cell 
with  nucleus,  the  latter  approaching  the  wall ;  6  to  h,  nucleus  elongating  and  curving 
into  an  arc,  and  finally  a  spiral  coil;  e,  an  edge  view,  showing  origin  of  cilia  from 
peripheral  protoplasm  ;  /,  also  an  edge  view;  k,  mature  sperm,  free.  Magnified  iooo 
diam. — After  ( luignard. 

tains    a   sperm;    so    that    each    spermary    produces    20,000- 
40,000  sperms. 

384.  Mossworts  and   fernworts. — In  the    mossworts   the 

spermary  is  a  stalked  body,  whose  internal  cells  are  the  sperm 
mother  cells,  the  outer  laver  forming  the  spermary  wall  (fig. 

In  the  fernworts  the  spermary  is  sessile  and  the  number  of 
mother  cells  is  much  smaller  (fig.  314),  corresponding  to  the 
reduction  in  size  of  the  gametophyte  (see  •  395)-  When 
the  gametophyte  is  greatly  reduced,  as  in  the  club-mosseSj 
a  single  spermary  only  is  formed,  which  is  even  larger 
than  the  rest  of  the  gametophyte  (fig.  315). 

385.  Seed  plants.  —  In  the  seed  plants  the  male  gameto- 
phyte begins  to  be  formed  before  the  microspore  leaves  the 
sporangium.  In  gymnosperms  the  spore  divides  into  two  to 
six  cells,  one  or  two  of  which  represent  the  vegetative  part 


SEXUAL   REPRODUCTION. 


28l 


Chara.  bear- 


ol"  the  gametophyte  and  the  others  the  spermary  (fig.  316). 
In  angiosperms  the  vegetative  part  seems  to  have  vanished 
and  the  two  cells  which  are  formed  constitute  the  spermary, 
the  smaller  representing 
the  sperm  cells  and  the 
larger  the  wall  cells  (fig. 
317;  compare  fig.  315). 
Sometimes,  indeed,  the 
smaller  cell  is  only  repre- 
sented by  a  nucleus,  no 
partition  wall  being  pres- 
ent. Thus,  the  spermary 
in  all  seed  plants  has  almost 
become  a  simple  one  again 
by  reduction  from  the  com- 
pound spermary  of  their 
ancestors 

reduction  of  the  male  game- 
tophyte,  that  is,  to  a  sex 
organ  alone,  almost  all  trace 
of  resemblance  to  a  plant 
has  been  lost,  and  it  is  diffi- 
cult to  think  of  the  pollen- 
grain  (microspore)  as  pro- 
ducing a  real  plant.  This 
male  plant,  though  ex- 
tremely small  and  simple 
even  when  mature,  is  the 
exact  homologue  of  the 
larger  male  plant  produced 
by  the  spores  of  the  mosses,  ferns,  horsetails  and  selaginellas. 
386.  Pollen  tube.  -The  maturity  of  the  male  gametophyte 
is  reached  only  alter  the  microspore  has  been  caught  by  the 
moist  surface  |  fluid  in  the  micropvle  or  on   the   stigma  |  pro- 


By  this  extreme  Fig.  313.— A,  part  of  a  "leaf 

ing  sexual  organs.  /\  leaf;  p.  undeveloped 
"leaflets";  0',  leaflet;  /3",  leaflets  of  the 
branch,  sc;  the  dark  oval  body  is  the  ovary 
containing  the  fertilized  egg;  ,v,  five  cortical 
cells  which  have  grown  spirally  around  the 
ovary  proper  and  become  adherent  to  it ; 
they  terminate  in  .  ,  the  five  crown  cells,  be- 
tween which  the  sperm  makes  its  way  to  the 
egg;  ,1.  the  spermary,  showing  four  of  the 
s  toothed  plates  of  which  its  wall  is  composed, 
and  the  center  ot  each  to  which  on  the  inside 
the  handle  cell  is  attached.  Magnified  33 
diam.  /•'.  longitudinal  section  through  young 
"node"  of  a  "leaf  "  of  ( lhara,  showing  origin 
and  young  stage  ot  sexual  organs.  /  and  in 
stand  in  the  c  omers  ot  the  adjacent  tnternodal 
.ells;    between    them   is  the  thin  nodal  cell 

from  which   arise    ;<   and   the  sexual  organs  .vX- 
and  ,1  ;    br,  cortical   tells  co 
is  the  young  ovary  not  yet  overgrown  by  the 
cortical  cells  at  its  side's.    ,,.  the  spermary, 

shows  four  wall  cells  outside,  from  which 
their  handle  cells  have  just  been  divided; 
all  too  young  to  shew  relative  sizes  or  shapes. 
Magnified  2 1"  diam      Alter  Sat  hs. 


282 


PLANT  LIFE. 


vided  to  receive  it.  The  wall  cell  remains  undivided  and 
grows  to  form  an  unseptate  filament,  called  the  "pollen 
tube"  (figs.  317,  318,  319,   321,    322,   323).     In   gymno- 


Fig.  314. 

Fig.  314. — Vertical  median  section  of  the  mature  spermary  of  a  fern  [Adiantutn 
capillvs-veneris).  /.  adjacent  cells  of  gametophyte  (figs.  74,  77)  j  ,(,  spermary,  show- 
ing wall  composed  of  three  cells,  the  two  lower  (above  and  below  letter  a)  being  ring- 
like. The  chloroplasts  have  accumulated  on  the  inner  face.  The  interior  cell,  origi- 
nally single,  has  divided  into  a  number,  the  sperm  mother  cells,  which  at  this  stage  are 
loosened  and  contain  each  a  fully  developed  coiled  sperm.  Magnified  550  diam. — 
After  Sachs. 

Fig.  315. — A  vertical  median  section  of  the  gametophyte  of  Selaginella  stolonifera. 
/>,  a  single  cell  representing  the  vegetative  part  of  the  gametophyte  (compare  figs.  74, 
314)  ;  w,  the  cells  forming  the  wall  of  tile  spermary;  ,f,  the  mother  cells  of  the  sperms, 
each  containing  one  sperm  and  now  loosened  from  each  other.  The  gametophyte  with 
its  single  spermary  scarcely  exceeds  the  size  of  the  microspore  which  produces  it  and 
therefore  only  just  bursts  the  outer  wall  of  the  spore.  The  solution  of  the  wall  cells 
w  allows  the  sperms  to  escape.     Magnified  640  diam. — After  Strasburger. 

Fig.  316.— Diagram  of  the  gametophyte  of  the  larch  (Larijc  Europaa),  formed  in  the 
microspore.  /,  the  vegetative  cell  ;  st ,  two  stalk  cells  of  the  spermary;  s,  cell  whose 
nucleus  subsequently  divides  to  form  two  sperms  (the  walls  of  the  mother  cells  not 
forming) ;  w,  the  wall  of  the  spermary  which  remains  undivided.     Compare  fig.  315. 

sperms  this  penetrates  the  megasporangium  (ovule  body)  and 
reaches  the  female  gametophyte  on  whose  surface  are  formed 
the  ovaries  (figs.  319,  320,  321,  322).  In  the  course  of  its 
development  the  sperm  cell  loosens  itself  and  migrates  down 
the  tube.  Its  nucleus  is  set  free  by  the  disorganization  of  the 
wall  of  the  cell  (if  formed)  and  usually  undergoes  division, 
thus  making  two  or  more  sperms  (figs.  321,  322).  These 
escape  through  the  ruptured  wall  of  the  end  of  the  tube, 
pass  between  the  neck  cells  of  the  ovary  and  so  fertilize  the 

egg  (11  39 3>  fig-  32i)- 

In  angiosperms,  in  order  that  the  sperm  may  reach  the 
egg,  the  pollen  tube  must  grow  through  the  tissues  of  the 
stigma  and  style,  or  pass  down  the  style  canal  to  the  interior 


SEX  UA  L   REP  ROD  UCTION. 


283 


of  the  ovulary,  then  through  the  micropyle  (fig.  323),  and 
finally  penetrate  the  megasporangium.  The  sperm  nucleus 
then  fuses  with  the  egg  nucleus  (see  ^[  369). 


Fig.  317- 


Fig.  31 


Fig.  319. 


Fig.  317. — Gametophyte  of  the  pinesap  (Monotrofla  Hypopitys).  <?,  microspore  show- 
ing two  cells;  the  smaller  being  the  sperm  cell  and  the  larger  corresponding  to  the 
wall  of  the  spermary,  undivided.  /■.  the  same,  6  hours  later,  showing  the  pollen  tube 
developed  from  the  larger  cell.  The  smaller  one  has  become  disorganized  ami  its 
nucleus  isttll  undivided  into  sperms!  and  that  of  the  larger  cell  have  migrated  into  the 
tube.     Magnified  too  diam. — After  Strasburger. 

FlG.  318. — One  stage  in  the  fertilization  of  the  egg  of  an  orchid  {Orchis  latifolta).  The 
pollen  tube,  /»,  has  entered  the  narrow  micropyle,  «/,  of  an  ovule,  and  reached  the 
megaspore  e,  the  upper  half  of  which  only  is  shown  with  three  eggs  (two  imp  rfi  1 1), 
In  the  pollen  tube,  just  above  and  below  the  entrance  of  the  micropyle,  are  the  two 
sperms,  s.  s' .     Magnified  3in.di.1m.     After  Strasburger. 

1  1  11.  Longitudinal  section  through  the  ovule  oi  the  larch  and  the  placental  scale 
to  which  it  is  attached.  /,  placental  stale;  ^,  vascular  bundles;  ;/.  megasporangium  ; 
i,  integument;  .  ,  female  gametophyte  inside  megaspore  wln.se  limit  is  shown  b)  oval 
line;  ,;,  ovary;/,  pollen-tube.     Magnified  14  diam. — After  Strasburger, 


The  growth  of  the  spermary  as  a  tube  within  which  the 
sperms  may  migrate  to  the  egg  is  necessary  because  the  female 
gametophyte  is  forced  to  develop  within  the  megaspore, 
which  is  not  released  from  the  sporangium.  In  angiosperms 
the  further  enclosure  of  the  megasporangia  in  the  sporophyll 
(carpel)  makes  it  necessary  for  the  tube  to  be  sufficiently  long 


284 


PL A. XT  LIFE. 


to  traverse  the   pistil.      Pollen  tubes  may,   therefore,    grow 
10-15  cm.  in  length.      Usually  the  older  part  of  the  tube  dies 


Fig.  322. 


Fir,.  320. — Anterior  fourth  of  female  gam'etophyte  of  spruce  {Picea  exceka),  showing 
two  ovaries.  <\  tissue  ot  gametophyte  (endosperm);  a,  egg;  k.  nucleus  oi  egg;  /;, 
neck  of  ovary  (the  line  does  not  reach  the  neck,  which  is  situated  in  a  depression  of  the 
plant  below  //  :  the  shading  shows  the  side  (d  this  slope);  kz,  neck  canal  cell.  See  fig. 
321.     Magnified  50  diam.  -After  Strasburger. 

Fig.  321.— A  portion  of  the  ovary  of  the  spruce,  seen  as  in  fig    j  ■■    but  magnified  165 

diam.  The  cell  kz  of  lie,.  320  has  bei  mm  .h  -.  u  j.ini/ed  to  make  way  for  the  pollen 
tube,/,  which  has  pushed  between  the  neck  cells  and  reached  the  egg,  r,  into  which 
one  of  the  sperms  in  its  tip  is  about  to  enter,  g,  tissue  of  the  female  gametophyte.— 
After  Strasburger. 
Fig.  322.  Upper  part  of  ovule  of  red  cedar,  with  integument  removed.  >ni,  mega- 
sporangium  ;  ctl,  female  gametophyte  with  three  ovaries  oi  .11  luster  of  six  ;  /,  pollen 
tube.  Each  ovary  shows  an  elongated  egg  and  above  the  small  neck  cells.  The  left- 
hand  pollen  tube  has  two  sperms  about  to  pass  between  neck  cells  into  an  egg.  Magni- 
fied 67  diam.— After  Strasburger. 


as  the  tip  advances.     The  food  needed   is  chiefly    derived 
from  the  cells  of  the  stigma  and  style  which  it  disorganizes. 


SEXUAL   REPRODUCTION. 


285 


387.   The  egg. — The  egg  is  larger  than  the  sperm,  usually 
non-motile  and  fixed.      In  aquatic  algre  the  egg  is  sometimes 


Fig.  323. — Diagram  of  a  lun^iti.iuni.il  >cl tii.n  of  a  pistil  with  one  ovule,    s,  stigma,  on 
which  are  lodged  two  pollen  grains ;  ;  .  style  ;  a,  01  ulary ;  /.  >/,  at,  //,  together  form 

the  Ovule  ;  /,  stalk  ;  //,  niega>poi,mgium  ;  ,; /',  outer  integument  ;  //.  inner  integument  ; 
r.  megaspure.  will)  nucleus  which  is  to  develop  later  into  vegetative  part  ol  female 
plant;  i,  antipodal  cells ;  k,  egg,  and  near  by  another ;  m,  micropyle  j  /,  polli 

entering  it  and  reaching  egg.  -Alter  I.ucrssen. 

free,  escaping  from  the  ovary  in  which  it  is  produced,  and 
being  fertilized  by  the  sperms,  which  arc  likewise  tree  in  the 
water,  as  in  Fucus  (fig.  324).  Sometimes  the  egg  itself  is 
ciliatedand  hence  motile.  In  these  cases  it  meets  the  motile 
sperms  in  the  water. 

The  form  of  the  egg  is  much  less  variable  than  that  of  the 


(86 


PLANT  LIFE. 


sperm.  It  is  almost  always  ovoid  or  globular.  The  small 
amount  of  body  protoplasm  of  the  sperm  may  be  looked  upon 
as  merely  accessory.  That  of  the  egg,  however,  is  usually 
abundant  and  well  supplied  with  reserve  food,  and  it  takes 
part  after  fertilization  in  the  formation  of  the  new  plant. 

388.  The  ovary. — The  organ  in  which  theegg  is  produced 
is  the  ovary  (oogonium,  carpogonium,  or  archegonium). 
Usually  but  one  egg  is  produced  in  each  ovary,  though  as 
many  as  eight  are  formed  in  the  Fucacere 
(fig.  327).  The  ovary  is  either  simple 
or  compound. 

389.  A  simple  ovary  consists  of  a 
single  cell,  the  bulk  of  whose  proto- 
plasm   becomes  one  egg  (or   several)..       ($ 


324.  Fig.  325. 

Fig.  324. — Egg  of  Fiichs  as  it  floats  in  sea-water,  surrounded  by  many  sperms,  one  of 
which  eventually  plunges  into  it,  unites  with  its  nucleus  and  so  fertilizes  it.  Magnified 
350  diam. — After  Thuret. 

Fi<;.  325. — Portion  of  two  ovaries  of  an  alga  {Spkeerofilea  annulina).  The  upper  part 
contains  two  eggs,  and  a  number  of  sperms  which  have  entered  through  the  pore  at 
the  side.  The  lower  egg  of  the  two  shows  the  receptive  spot  above.  A  sperm  is 
partially  imbedded  in  the  protoplasm  of  this  part  in  process  of  fertilization  The 
egg  in  the  lower  ovary  has  been  fertilized  and  has  secreted  a  thick  wall,  thus  becom- 
ing a  resting  spore.      Magnified  500  diam. — After  Colin. 


A  portion  of  the  protoplasm  of  the  ovary  is  almost  invariably 
excluded  from  the  egg  (B,  fig.  308).  The  sperms  reach  the 
egg  either  through  an  opening  formed  in  the  wall  of  the 
ovary  (D,  fig.  308,  325),  or  through  a  tube  formed  by  the 
spermary,  which  penetrates  the  ovary  (fig.  307). 


SEX  UA  L   REPR  OD  U  CTION. 


287 


Simple  ovaries  occur  only  in  the  algseand  fungi,  where  they 
are  known  as  oogonia  or  carpogonia.  They  are  either  pro- 
duced by  the  modification  of  one  of  the  cells  of  a  filament 
(fig.  325),  or  they  are  the  terminal  cell  of  a  special  branch 
(fig.  308).  Usually  the  ovary  is  decidedly  larger  than  the  or- 
dinary vegetative  cells.  The  fertilized  egg  often  becomes  a 
resting  spore  (fig.  325). 

in  the  higher  algae,  especially  the  marine  algae,  the  ovaries 
are  often  aggregated  in  special  pits,  the  conceptacles,  as  in 


m 


Fig.  326.- A  section  through  a  female  conceptacle  of  bladder  wrack  (Fucks  vesiculo- 
sits);  showing  form  <il  pit.  the  numerous  hairs  with  which  it  is  lined,  and  ovaries  in 
various  stages  . .  t  development.  In  the  tissue  about  the  pit  note  the  cortex  oi  densely 
plated  cells  and  the  loose  network  of  filaments  in  the  interior.  Magnified  50 diam. — 
After  Thuret. 

Fucus  (figs.  42,  326).  Here  the  ovary  is  formed  by  the  en- 
largement of  the  terminal  cell  of  a  two-celled  outgrowth  from 
the  surface  (\'\y;.  327).  The  eight  eggs  are  set  free  and  are 
fertilized  in  the  water  1>\  the  motile  sperms  (fig.  324).  They 
grow  at  once  into  new  plants. 

The  simple  ovary  is  surrounded  in  Chara  (fig.  313)  by  a 
jacket  of  spirally  coiled  cells,  which  grow  up  from  beneath  it 
and  make  it  look  as  though  it  were  compound  (•'  390). 


288 


PLANT  LIFE. 


The  most  highly  developed  simple  ovary  (the  carpogonium) 
occurs  in  the  red  algae,  in  which  it  is  often  differentiated  into 
the  ovary  proper  (which  does  not  always  form  a  distinct  egg  | 
and  a  long  branch,  the  receptive  apparatus,  or  trichogyne, 
to  which  the  sperm  adheres  and   through  which  its  nucleus 


Fig    329. 

Fig.  327.  Ovary  of  bladder  wrack  (Funis  vesicuiosus),  with  some  of  the  hairs.  The 
ovary  is  raised  on  a  stalk  cell ;  it  contains  8  eggs,  of  which  6  are  shown.  Magnified 
160  diam.     After  Thuret. 

Fig.  328.— The  ovary  of  a  red  alga  {Nemalion  multifidum).  A ,  in  process  of  ferti- 
lization, rco,  egg  nucleus  (a  dark  chromoplast  lying  near);  sp,  sperm  which  has  ad- 
hered to  the  trichogyne  t  and  caused  the  absorption  of  the  wall  there  :  ns,  the  sperm 
nucleus  on  the  way  down  the  iii.  Imumh-  /•'.  ,1  later  stage,  no  and  ns  about  to  unite. 
Magnified  about  600  diam. — After  Wille. 

I'ii.  \    In. null    nt  .1  red   sf.iweed  (  rolyslfihoniti    ofiaca)  bearing  cystocarps   (the 

black  dots).    See  fig.  330.     Natural  size. — After  ECUtzing. 


travels  to  the  ovary  proper  (fig.  328).  The  result  of  fertiliza- 
tion is  the  production,  often  by  a  very  complicated  process 
of  growth,  of  a  spore-producing  body,  the  cystocarp  (figs. 
329,  330).  The  cystocarp  is,  in  part,  the  homologue  of  the 
sporophyte   phase  of  higher   plants.      From   its  interior  non- 


SEX UA  L   RE  PR OD  UCTION. 


289 


sexual  spores  arise  (fig.  330),  which  produce  the  gametophyte 
again. 

390.   A  compound  ovary  consists  of  a  central  row  of  cells 
(each  of  which  is  homologous  with  a  simple  ovary)  surrounded 


Fig.  330. — A ,  a  bit  of  a  red  seaweed  bearing  a  mature  cystocarp  ;  seen  from  the  side. 
The  spores  show  through  the  translucent  wall.  />'.  a  diagram  of  a  section  through  the 
same,  showing  spores  as  enlarged  terminal  cells  of  twigs  arising  from  a  basal  cell  of  the 
cystocarp.  The  shaded  parts  arise  from  the  fertilized  egg  (=  a  sporophyte),  the  case 
developing  by  induced  growth.     Magnified  25  diam. — After  Falkenberg. 

by  a  wall  composed  of  one  or  more  layers  of  cells.  Of  the 
central  cells  only  the  lowest  produces  an  egg.  The  upper 
ones  break  down  into  mucilage,  by  the  swelling  of  which  the 
ovary  is  opened,  and  by  its  escape  in  whole  or  part  a  canal  is 
formed  leading  to  the  egg  (fig.  332).  Down  this  canal  the 
sperms  make  their  way,  and  one  fertilizes  the  egg. 

The  compound  ovary  is  known  as  an  archegonium.  When 
best  developed,  it  is  a  flask-shaped  structure  [f\i;.  331)  con- 
sisting of  a  body  and  a  neck.  In  the  body  is  the  cell  con- 
taining the  egg.  Compound  ovaries  may  be  stalked,  sessile, 
or  sunk  in  the  tissues  of  the  gametophyte.  They  are  found 
only  in  mossworts,  fernworts,  ami  seed  plants.  In  the  latter. 
however,  they  are  simplified  out  of  all  likeness  to  the  form 
dese  lilted. 

391.  Mossworts. — When  the  gametophyte  is  differentiated 
into  stem  and  [eaves,  as  in  mossworts  alone,  they  are  formed 
upon  the  stem.  Usually  several  are  developed  in  the  same 
neighborhood,  when  they  are  generally  protected   by  over- 


290 


PLANT  LIFE. 


arching  leaves  (fig.  331).  In  the  same  cluster  there  may  be 
spermaries,  or  these  may  be  on  a  different  part  of  the  same 
plant,  or  on  another  plant. 


Fig   33" 


Fig.  332. 


Fig.  331.— Longitudinal  section  through  the  tip  of  a  shoot  of  a  moss  (Funaria  hygro- 
metrica).  st,  stem  ;  />,  leaves  protecting  the  ovaries  a.  Magnified  ioo  diam.— After 
Sachs. 

Fig.  332. — A  vertical  section  of  the  gametophyte  of  a  fern  ( Pteris  serrulata).  g,  vege- 
tative tissue  of  gametophyte,  with  chloroplasts ;  e, .body  of  ovary  sunk  in  gameto- 
phyte. surrounding  the  spherical  egg;  «,  neck  projecting  and  curved;  /«.  mucilage 
formed  by  disorganization  of  canal  cells  and  escaping,  having  pushed  apart  terminal 
cells  of  neck.     Magnified  260  diam. — After  Strasburger. 

392.  Fernworts  and  seed  plants. — When  the  gametophyte 
is  a  thallus,  as  in  fernworts  and  seed  plants,  the  ovaries  are 
borne  on  the  surface  of  the  thallus,  partially  or  wholly  sunk 
in  its  tissue.  In  the  ferns,  they  arise  upon  the  under  surface, 
near  the  anterior  end  (fig.  74),  and  have  the  neck  only  pro- 
jecting (fig.  332).  In  the  horsetails  the  ovary  is  still  more 
deeply  sunk.  In  the  selaginellas  the  gametophytes  are  male 
and  female,  the  male  arising  from  the  microspores  (fig.  315) 
and  the  female  from  the  megaspores  (fig.  333).  Both  are 
small,  scarcely  larger  than  the  spores  in  which  they  grow. 
The  ovary  is  completely  sunk  in  the  female  gametophyte  and 


SEXUAL    REPRODUCTION. 


29I 


is  much  simplified,  the  neck-cells  and  the  egg  being  the  only 
distinct  parts  of  maturity. 

393.    Gymnosperms. — In    the    gymnosperms   the    female 
gametophyte  is  not  large  enough  to  burst  the  megaspore  which 


spin 


Fig.  333.  — Longitudinal  section  of  the  female  gametophyte  of  Selaginella  Martensii. 
//,  d,  (/,  the  body  of  gametophyte;  »-,  r,  rhizoids  (rudimentary)  on  its  surface;  a,  an 
Ovary  whose  egg  failed  of  fertilization;  e,  embryo  developed  from  fertilized  egg;  its 
Cell-structure  is  not  shown,  but  the  various  members  are  begun  ;  .r,  suspensor  ;  st,  stem; 
/,  /,  primary  leaves  ;  rt,  root;  /,  foot ;  e ',  a  younger  embryo,  with  cell-structure  shown, 
the  letter  standing  in  large  suspensor  cell ;  spnt,  wall  of  megaspore.  Magnified  12c 
diam.- After  Ffeffer. 


remains  enclosed  in  the  sporangium.  Upon  its  surface  are 
formed  several  ovaries,  each  reduced  to  an  egg  and  two  to  four 
tiers  of  neck-cells  (figs.  320,  321). 

394.  Angiosperms. — In  the  angiosperms  the  female  gam- 
etophyte is  so  simplified  that  it  is  represented  only  by  a  few 
cells,  among  which  may  be  recognized  at  least  one  egg  (e, 
fig.  334),  and  possibly  two  others,  s,  s.  The  ovary  has  been 
reduced  to  nothing  but  an  egg,  and  the  full  development  of 
the  gametophyte   seems   to  be  delayed  until  after  the  egg  is 


292 


PLANT   LIFE. 


fertilized.  In  these  plants,  therefore,  we  return  to  a  con- 
dition which  is  scarcely  an  alternation  of  sexual  and  spore- 
producing  phases,  because  the 
sexual  phase  is  nearly  obliterated 
by  reduction. 

395.  Relative  size  of  gameto- 
phyte  and  sporophyte. — The  ac- 
companying diagram  (fig.  335)  may 
roughly    illustrate     the    history    of 


Fig.  334. 


Fig.  335- 


Fig.  334.— End  oi  megaspore  ol  I\<Iy^ouii ///  liivaricatum.  e,  egg;  s,  s,  synergi- 
dx,  probably  sterile  eggs.  Below  e  the  nucleus  from  whose  divisions  arise  the  cells 
"I  the  belated  gametophyte      Magnified  540  diam      Alter  Strasburger. 

Fio  J35  Diagram  representing  the  reduction  of  gametophyte  and  increase  in  sporo- 
phyte from  lower  to  higher  plants,  a,  green  alga-  ;  /-,  red  alga-:  r.  liverworts;  </, 
mosses;  e,  ferns  ;  y,  club-mosses;  .i,-,  gymnosperms  ;   /;.  angiosperms.     Original. 

development  of  these  phases  in  the  vegetable  kingdom. 

The  gametophyte  phase  is  represented  by  the  dotted  area. 
It  has  its  greatest  development  in  the  lower  algse  and  fungi, 
where  it  constitutes  the  whole,  diminishes  at  first  slowly  and 
then  rapidly.  After  the  fernworts  are  passed  it  constitutes  a 
relatively  inconsiderable  part  of  the  plant  and  almost  disap- 
pears among  angiosperms.  Of  the  sporophyte,  represented 
by  the  white  area,  the  reverse  is  true.  The  lines  (tossing 
the  diagram  at  various  levels  show  by  their  length  in  the 
white  and  black  areas  the  relative  importance  of  the  two 
phases  in  the  groups  indicated. 


SEXUA  L    REPROD  UCT10N. 


293 


Loss  of   sexuality. 


396.  Among  fungi. — Though  descended  from  ancestors 
possessing  sexual  organs, certain  groups  of  plants  have  lost  this 
mode  Ox"  reproduction  and  rely  wholly  upon  non-sexual 
methods.  Such  are  the  higher 
fungi.  The  lower  forms  only 
have  sexual  organs.  These  fungi 
show  their-  relation  to  algae  by 
retaining  in  part  or  wholly  aqua- 
tic habits.  In  Cysiopus,  for  ex- 
ample, at  a  certain  stage  zo- 
ospores are  produced  ;  and  these 
are  generally  characteristic  of 
aquatic  plants,  though  Cystopus 
has  become  a  parasite  upon  land 
plants.  Many  aquatic  fungi  are 
known,  most  of  which  grow 
upon  dead  plants  or  animals 
(espe<  ially  insects)  which  have 
fallen  into  the  water.  Not  only 
do  many  of  these  lower  forms 
produce  zoospores,  but  the  form 
of  their  sex-organs  and  mode 
of  union  remind  one  immedi- 
ately of  similar  structure  and 
action  in  common  algae.  Com- 
pare, for  example,  the  sex- organs 
in   Vaucheria  (fig.  308)  and  those  oi  Achlya  (fig.  336). 

Some  fungi  possess  sex-organs  which  are  functionless, 
although  the  egg  de\  elops  as  though  it  had  been  fertilized  I  fig. 
336).  But  in  most,  all  trace  of  sexual  organs  has  disappeared, 
though  many  produi  e  spore-bearing  structures,  the  fructifica- 


Fig.  336. — A.  Functionless 
of  a   fungus     (Achlya     <■ 

with  'i  eggs  . 
spermaries  from  branches  ol  same 
liyplia  form  fertilizing  tube  which  re- 
mains closed.  /•'.  eggs  which  have 
tini;  spuii's  w  itliout  ferti- 
lization. M.i.unilu-il  .■!•-•.  iliam. — After 
s.n  hs. 


294  PLANT  LIFE. 

tions  (c  314)  which  are  homologous  with  those  known  to  arise 
from  the  fertilized  egg  and  adja<  ent  parts.  In  all  these  cases 
the  fructification  may  be  considered  the  homologue  of  the 
sporophyte  of  higher  plants,  for,  even  though  its  origin  is 
now  purely  vegetative,  this  has  come  about  by  reduction  from 
more  perfect  ancestors. 

397.  Apogamy. — In  certain  of  the  higher  plants  sexual  re- 
production is  sometimes  replaced  by  a  process  of  budding, 
which  differs  from  reproduction  by  brood  buds  (c  361  ff . ) 
in  giving  rise  to  the  other  phase  from  that  on  \vhi<  h  the  bud 
arises.  Some  ferns,  for  example,  regularly  produce  upon  the 
gametophyte  a  bud  which  grows  into  a  sporophyte,  the  sex- 
organs  being  functionless.     This  process  is  called  apogamy. 

398.  Polyembryony. — Among  the  seed-plants  a  budding 
of  the  megasporangium,  instead  of  the  fertilization  of  the  egg, 
ma}-  produce  an  embryo.  Except  that  the  embryo  so  pro- 
duced suspends  its  growth  and  becomes  a  part  of  a  seed,  such 
reproduction  is  in  no  way  different  from  that  by  brood  buds 
(^[  361  ff.)  It  is  common  in  the  orange,  and  often  results  in 
the  formation  of  more  than  one  embryo  in  the  seed. 

Results  of  sexual    union. 

The  immediate  result  of  the  coalescence  of  a  male  and  a 
female  gamete  is  the  formation  of  a  cell  capable  of  producing 
a  new  plant,  i.e  .  a  spore.  The  first  step  toward  this  is  the 
formation  of  a  wall  about  the  spore.  It  may  then  grow  at 
once  into  a  new  plant,  or  it  may  remain  dormant  for  a  longer 
or  shorter  time. 

399.  Resting  spores. — In  the  latter  case  it  is  called  a 
"resting  spore."  To  protect  itself,  it  thickens  its-wall,  often 
very  greatly.  It  may  then  escape  from  the  parent  by  the 
breaking  of  the  ovary  in  which  it  lies,  but  more  commonly  it 
remains   enclosed   until  set   free  by  the  death  of  the  parent 


SEXUAL   REPRODUCTION.  295 

and  the  decay  of  the  ovary.      Such  are  the  resting  spores  of 
Spirogyrciy  Mucin-,  Cystopus,  and  Chara.* 

400.  Embryo.  —  In  the  other  case  the  sexually  produced 
spore  develops  at  once.  Except  in  the  brown  seaweeds, 
whose  eggs  are  ejected  into  the  water  before  fertilization,  the 
spore  remains  enclosed  in  the  ovary,  within  which  it  begins 
to  form  an  embryo. 

401.  Induced  growth. — As  a  consequence  of  this  develop- 
ment, growth  is  induced  in  the  ovary  itself  and  the  parts 
adjacent.  In  the  mildews  the  ovary  produces  one  or  more 
asci  (fig.  224),  while  the  hyphae  near  by  branch  profusely  and 
cover  the  developing  internal  parts  with  a  thick  false  tissue 
(figs.  223,  337),  the  whole  constituting  a  fructification.      In 


Fig.  337. — Formation  of  t he  "  fruit"  in  a  mildew  (Rrysiphe  Cichoriacearum).  a, 
threads  of  mycelium  ;  i,  spermary  ;  r,  ovary  ;  </.  the  ovary  after  fertilization,  show- 
ing tin  branches  from  hypha  beneath  ovary  covering  it;  e,  later  stage,  showing 
these  branches  coalescent  and  dividing  by  partitions  to  form  a  false  tissue.  (Com- 
pare fig.  223.)      Highly  magnified. —  After  <  Ersted. 

red  seaweeds  the  ovary  and  adjacent  parts  finally  form  the 
cystocarp  (fig.  330).  In  mosses  the  ovary  grows  extensively 
(fig.  33$),  but  is  finally  torn  loose  and  carried  up  on  the 
embryo  and  becomes  the  loose  hood,  which  is  usually  lost 
early.  The  stem  also  enlarges  beneath  the  ovary  and  forms 
a  sheath  around  the  embryo  (fig.  338),  which  grows  down- 
ward into  the  parent  though  not  organically  connected  with 

*It  should  be  remembered  that  thick-walled  "resting  -ion-"  arc  also 
formed  vegetatively.     Sec  ■    jo8 


ig6 


PLANT  LIFE. 


it.      At  the  same  time  the  neighboring  leaves  are  stimulated 
to  increased  growth. 

In  fernworts  the  sexual  plant   is  stimulated  by  the  growth 

of  the  embryo  within   it,  and  enlarges  considerably. 

But  it  is  soon  outgrown  by  the  young  sporophyte, 

to    which   it  supplies   nourishment  until   leaves  are 

produced  and  it  is  able  to  feed  itself  (figs.  76,  77 

78). 

402.  Seed.— In  all  but  the  seed  plants  the  de- 
velopment of  the   embryo   is    uninterrupted   until 
a    mature     sporophyte     is 
formed.        In     seed-plants 
the   embryo   develops  to  a 
stage,     and     then 


Fig.  338.  Development  of  the  embryo  sporophyte  of  a  moss  {Funaria  hygro- 
metrica\  A,  longitudinal  section  ol  the  ovary,  <5,  £,  A,  shortly  after  fertilization 
of  egg  which  has  developed  into  the  embryo,  ol  which  J  is  the  apical  growing  point 
and  /'  the  b  isal,  or  foot  ;  /.,  /..  body  of  ovary  ;  //,  tile  base  of  the  neck.  /•',  longi- 
tudinal section  through  apex  of  stem  and  leaves.  Two  Ovaries  are  seen  ;  one  has 
failed  of  fertilization  ;  the  other,  c,  has  enlarged  I"  a<  i  ommodate  the  embryo,  _/",  de- 
veloping inside  it  ;  //.  its  neck,  now  withered.  ( ',  longitudinal  section  of  same,  older; 
f,  the  embryo  has  grown  downward  into   the  apex   ot    sirni  :   tin-   ovary,  .  .  has  still 

further  enlarged  and  indeed  outgrow  n  the  embryo,  forming  a  bladdery  case  around 

its  base  and  elsewhere  a  close  sheath  for  it  ;  /;,  the  neck.  Around  the  embryo,  where 
it  enters  the  stem,  the  latter  has  grown  up  as  a  sheath  to  whose  edge  the  base  of 
ovarv  is  still  attached.  A  little  later  the  ovary  will  be  torn  off  at  this  point  and  will 
!„•  lifted  on  !h.  elongating  sporophyte  as  a  dry  membranous  sheath,  the  calyptra. 
.1 ,  magnified  500  diam.  ;  />'  and  C'  about  65  diam. — After  Sachs. 


SEXUA  L    RETROD  UCTION. 


297 


ceases  to  grow.      With  suitable  protection  and  food-supply 

it  is  then  cast  off  as  a  seed  (see  further  «[  408),  and  usu- 
ally after  a  dormant  period  continues  its  development  until 
mature. 

403.  In  gymnosperms. — The  growth  of  the  embryo  from 
the  egg  in  the  gymnosperms  stimulates  the  whole  gameto- 
phyte.  This  grows  as  rapidly  as  the  embryo,  which  pushes 
its  way  into  it  and  remains  completely  surrounded  by  it  (fig. 
339).  The  whole  ovule  is  also  stimulated  to  growth.  The 
sporangium  increases  for  a  time,  but  is  so  crowded  between 
the  growing  gametophyte  within  and  the  hardening  integu- 
ment without  that  it  is  mostly  absorbed  (fig.  339).  The  in- 
tegument grows  for  a  time 
to  accommodate  the  struc- 
tures within,  but  its  tissues 
finally  become  in  whole  or 
in  part  thick-walled,  form- 
ing the  seed- coat.  In  a  few 
gymnosperms     (Cycas)      its 


h 

Ki<;.  339.  Fig.  340. 

Fig.  33q. — Longitudinal  section  of  the  seed  of  silvrr  fir  i.//>/V.v  /V,  / 7 n.it, i\,  showing 

straight  embryo  with  several  primary  leaves  in  center  of  the  endosperm  (dotted); 

m,  the  micropyle,    The  integument  lias  become  the  testa  (shaded  with  radial  lines). 

Between  the  testa  and  endosperm  are  the  remains  of  the  sporangium.     Magnified 

about  5  diani       Alter  Kerner. 
FlG.  340.  —  Longitudinal  section  <il  seed  ,.1   ,  nail's.    //,  hilum  (scar  of  attach 

ment);  w,  micropyle ;   t,  outer  fleshy  layei   ol   integument;  //and   1V1,  two  hard 

layers,,)    same  ;  f,  thin  eap-like  remnant  of   sporangium  ;   /,  gametophyte   enlarged 

forming  the  1  ndosperm  :  ,».  eggs  which  faili  ,1  ol  I,  rtili/ation  ;  <-w,  embryo  produt  ed 
by  a  fertilized  egg.     Two  thirds  natural  size.     After  Luerssen, 

outer  parts  become  fleshy,  and  the  seed  looks  like  a  large 
cherry.  In  the  yew  a  second  fleshy  integument  (an  aril) 
grows  up  around  the  hard  seed  (fig.  247).  At  maturity  the 
seed  of  gymnosperms  thus  consists  of  the  embryo  within 
(fig.  340,  em)  surrounded  by  the  gametophyte,  />,  whose  cells 


298 


PLANT  LIFE. 


become  filled  with  reserve  food,  constituting  then  the  so-called 
endosperm;  around  this  is  the  remnant  of  the  sporangium, 
when  more  than  a  mere  membrane,  likewise  stored  with  food, 
and  <alled  the perisperm  ;  while  over  all  is  the  hardened  in- 
tegument or  iesta,  often  of  unlike  layers,  /,  if,  in. 

404.  Fruit. — In  the  conifers  the  sporophylls  hearing  the 
ovules  and  the  axis  from  which  they  arise  also  grow.  As  tin- 
ovule  is  becoming  the  seed  each  sporophyll  enlarges,  but 
especially  the  placental  out- 
growth (set'  •  334),  and  the 
whole  number,  together  with 
the  enlarged  axis,  form  the 
cone  (fig.  341,  358).  Some- 
times (as  in  the  junipers)  the 
sporophylls  become  fleshy  and 
adherent,  forming  a  berry-like 
body. 


34'- 


.;(-•• 


Fig.  341.— A  mature  cone  ol  .1  pine  (Pinus  sylvestris),  the  upper  quarter  cut  away. 
sq,  s</\  the  placenta]  si  ales  ;  g;  seeds  ;  <•«/,  embryo  in  a  seed,  lust  below  the  pla- 
cental  scale  which  bears  the  lower  seed  e,  may  be  seen  part  of  the  carpellary  scale 
in  section.     Magnified  about  2  diam.     From  liessey. 

Fig  342. — A  placental  scale  of  pine  {P.  sylvestris)  seen  from  above;  showing  two 
winged  seeds  in  place.  .1/,  micropyle  ;  «'//.  limit  oi  si  ed  ;  the  parts  beyond  are  Rat 
wings,  formed  by  the  splitting  off  of  a  layer  ol  tissue  from  the  surface  of  the  scale. 
Magnified  about   ;  diam.     Vtoxa  Bessey. 


SEXUAL    REPRODUCTION.  299 

When  firm  at  maturity  the  cone  scales  open  on  drying,  and 
the  seeds,  each  with  a  wing  attached,  split  off  from  the  scale 
(fig.  342)  and  are  shaken  out. 

405.  In  angiosperms  the  development  of  the  embryo 
stimulates  the  belated  female  plant  to  complete  its  growth, 
and  the  megaspore  (embryo-sac)  is  soon  entirely  filled  by  it. 
This  late-forming  gametophyte  is  called  endosperm,  as  in  the 
pines. 

406.  Endosperm. — The  growing  endosperm  and  the 
embryo  sporophyte,  which  it  surrounds,  crowd  upon  the 
sporangium.  This  may,  therefore,  partly  or  wholly  dis- 
appear. If,  when  the  full  size  of  the  endosperm  is  reached, 
the  embryo  continues  to  grow,  it  may  crowd  upon  the  endo- 
sperm until  a  part  or  all  of  it  is  absorbed.  The  embryo 
sooner  or  later  passes  into  a  resting  stage  and  ceases  to  en- 
large. In  this  dormant  condition  it  remains  for  a  time  whose 
duration  is  chiefly  determined  by  external  conditions. 

407.  Food. — The  tissue  of  the  endosperm  is  utilized  by 
the  parent  sporophyte  as  a  storehouse  of  food  for  the  use  of 
the  embryo  sporophyte  when  it  resumes  growth.  If  the 
embryo  displaces  the  endosperm,  it  absorbs  the  reserve  food 
therein,  consisting  of  starch,  oil,  or  aleurone  grains  (^[  236). 
In  case  any  tissue  belonging  to  the  sporangium  remains,  this 
also  is  utilized  for  storage.  To  distinguish  it  from  the  endo- 
sperm it  is  called  perisperm.  It  is  only  occasionally  present 
in  any  amount  in  this  group  of  plants. 

408.  The  integuments  of  the  ovule  at  the  same  time  en- 
large, and  finally  become  differentiated  in  such  fashion  as  to 
((institute  the  seed-coats.  The  ripened  seed,  therefore,  con- 
sists of  the  following  parts:  (  1  )  in  the  interior,  occupying 
various  positions  and  of  exceedingly  variable  relative  size,  the 
embryo;  (2)  immediate)  \  around  this,  the  endosperm  or  peri- 
sperm, or  both;  but  either  or  both  may  be  so  shrunken 
and  emptied  as  to  be  recognizable  only  by  microscopic  ex- 


300 


PLANT  LIFE. 


ami  nation  ;  (3)  upon  the  exterior,  one  or  two  integuments 
more  or  less  readily  distinguishable  from  each  other  (figs. 
343>  344,  345)- 


Fig.  743.— Longitudinal  section  of  fruit  of  black  pepper,  containing  a  single  seed.  /V, 
pericarp,  showing  two  layers  (the  outer  unshaded,  the  inner  shaded  by  radial  lines); 
sc,  seed-coats  ;  em,  embryo,  surrounded  by  en,  the  endosperm  ;  /,  perisperm.  Mag- 
nified about  5  diam. — After  Baillon. 

Fig.  344.— Seed  of  pansy,  entire  and  halved,  the  latter  showing  the  straight  embryo, 
the  endosperm  (white  and  dotted),  the  seed-coats  ;  m,  micropyle.  Magnified  about 
10  diam. — After  Baillon. 

409.  Fruit. — The  growth  of  the  embryo 
excites  not  only  the  tissues  of  the  ovule  to 
further  development,  but  also  the  sporophylls 
(carpels)  bearing  the  ovules,  and  not  infre- 
quently even  more  remote  parts.  The  carpels 
(PAytoiaVta  an<^  tne*r  contents  and  adherent  parts,  when 
halved* ^show'    fully  developed,  constitute  the  fruit.     The  car- 

b°rfoUnelt   the      Pe,s    are    tnen     knOWD    as    the    pericarp.       The 
and" neai-'b/sur5     changes   \vlii<  h   the   parts  undergo  are  chiefly 
"ndosperm!     of  two  sorts — an  increase  in  size  and  an  altera- 
dtam!  — ''After    ti011  °f  texture.      The  increase  in  size  requires 
no  special  explanation.      The  carpels   may  be- 
come dry  at   maturity,  or  may  thicken  and  become  soft  and 
fleshy,  or  even  juicy.      In  accordance  with   these  differences, 
two   sorts   of  fruits  are   recognized,   namely,   dry  fruits  and 
fleshy  fruits.      Between  these,  however,  there  is  no  sharp  line 
of  demarcation. 

410.   Dry  fruits. — If  the  pistil  contain  only  one  or  two 


SEXUAL   REPRODUCTION. 


30I 


seeds,  it  very  often  does  not  open  at  maturity.  Consequently, 
the  seed-coats  ordinarily  remain  thin,  and  the  protective 
function  is  put  upon  the  pericarp.  In  some  cases  the  carpel 
becomes  adherent  at  an  early  stage  to  the  surface  of  the 
ovule,  and  at  maturity  the  pericarp  is  so  firmly  attached  that 
it  can  scarcely  be  distinguished  from  the  seed-coats  them- 
selves. Such  a  change  takes  place  in  the  fruit  of  most  grasses, 
and  the  grain  so  formed  is  ordinarily  mistaken  for  a  seed 
(fig.  346).     When  dry  fruits  are  one-seeded  and  indehiscent 


12   34 


Fig.  346.— A  small  portion  from  the  margin  of  a  transverse  section  of  grain  of  oats, 
1,  2,  pericarp;  3,  seed-coats;  4,  remains  of  the  sporangium  :  5-7,  endosperm  ;  5. 
gluten  cells;  6,  cells  containing  large  compound  starch-grains  (compare  fig.  174)  at 
7  richer  in  gluten,  with  less  starch.     Magnified  about  325  diam.— After  Harz. 


the  pericarp  usually  bears  whatever  special  contrivances  are 
necessary  for  the  distribution  of  the  seeds.  (See  further  ^[ 
489  {{.^  If,  however,  the  pericarp  contains  many  seeds,  it 
generally  breaks  at  maturity  to  allow  the  loosened  seeds  to 
escape.  The  extent  and  position  of  the  opening  into  the 
seed  chamber  or  chambers  are  extremely  various.  In  some 
cases  the  openings  are  so  small  as  to  be  mere  slits  or  pores 
(fig.  347).  In  others  a  more  or  less  circular  line  of  breakage 
forms  a  little  door  or  valve  which  opens  and  closes  with 


302 


PLANT   LIFE. 


changes  of  moisture  (fig.  348).      In  other  cases  the  pericarp 
splits  lengthwise  into  two  or  more  pieces  (fig.  340),  or,  less 


Fig.  347. 


Fig.  348. 


Fig.  347. — Ripe  capsules  of  a  wintergreen  (Pyrola  c/itoran//ta),  showing  dehiscence 
by  pores.     The  opening  is  a  short  split  at  the  middle  of  the  base  of  each  carpel. 

Natural  size— After  Kerner. 
Fie;.  348.  —  Ripe  capsules   of   a   bellflower   (Campanula    ra/>u>uuloides),  showing 
small  reflexed  valves.     Natural  size. — After  Kerner. 


Fig.  34g.—/f,  capsule  of  violet  split  open  at  maturity,  the  seeds  still  attached  to  the 
parietal  placenta;.  />',  three  pods  of  Lotus  corniculatus ;  a,  just  beginning  to 
1  r,<.  k;  6,  split  throughout,  with  the  pie<  es  somewhat  twisted  ;  < ,  empty  ol  seeds,  the 
two  pieces  fully  dried  and  twisted.     Natural  size.— After  Baillon. 


SEXUAL    REPRODUCTION 


303 


often,  cracks  transversely  so  as  to  loosen  a  lid  (fig.  350).  In 
the  former  case,  if  it  is  composed  of  two  or  more  carpels, 
(1)  the  carpels  may  separate  from  each  other  along  their 
original  line  of  coalescence.  If  these  carpels  so  separated 
contain  only  one  or  two  seeds,  they  may  remain  indehiscent 
and  behave  like  the  simple  pistils  previously  described  ;  but 


Fig.  350. 

Fig.  350 — Ripe   capsule   of    pimpernell    {Anagallis   arvensis),   opening   by   a   lid. 

Magnified  several  diam. — After  Baillon. 
Fig.  351. — Diagrams  showing  three  modes  in  which  capsules  break  as  seen  in  trans- 

vt-rse  sections.     A,  septicidal  dehiscence;  B,  loculicidal  dehiscence  ;   C,  septifragal 

dehiscence.     Modified  from  Prantl. 

if  they  contain  several  to  many  seeds,  they  also  break  along 
their  inner  edges  (A,  fig.  351).  Or,  (2)  the  carpels  may 
split  along  the  middle,  ami  also  at  the  center  of  the  ovulai  v 
if  it  is  more  than  one-chambered  (B,  fig.  351  ;  A,  fig.  349). 
Or,  (3)  the  outer  parts  of  the  carpel  may  split  away  from  the 
placentae,  thus  exposing  the  seeds  (C,  fig.  351). 

411.  Fleshy  fruits. — The  changes  which  produce  fleshy 
fruits  consist  in  the  transformation  of  certain  parts  of  the 
pericarp  into  masses  of  thin- walled  juicy  cells.  Other  parts 
may  remain  unchanged,  or  may  even  become  hardened.  The 
inner  part  ot  the  pericarp  sometimes  becomes  of  a  stony 
hardness,  while  the  outer  portion  becomessoft  and  juicy.     Such 


304 


PLANT   LIFE. 


changes  produce  a  fruit  like  that  of  the  peach  or  the  cherry. 
The  pericarp  encloses  a  single  seed 
with  delicate  brown  seed  coats  whose 
protective  function  has  been  com- 
pletely usurped  by  the  stone  (fig. 
352).  In  other  cases,  while  the 
inner  face  becomes  stony,  the  outer 
becomes  fibrous,  tough,  and  dry,  as 
in  the  almond,  walnut,  and  hickory 
nut.      The  outer  part  in  the  last  even 


Fig.  352.— Fruit  of  the  cherry,  breaks    regularly    into    four    pieces 

halved,     e,  epidermis  of  peri-  _,_....                         .    .            _ 

carp;     m,     fleshy     layer     of  Such    frUltS   flimisll    a    transition     frOU 
pericarp ;    en,  stony   layer  of 


pencarp;  .?,  seed;  cot,  one    the  most   perfect    fleshy  fruits  to   the 

of  the  pair  of  thickened  seed-  .  . 

leaves  of  embryo.    Natural   dry  fruits.    In  other  cases  the  placentas 

size. — After  Focke.  .  , 

become  very  much  enlarged,  and  the 
whole  of  the  pericarp  becomes  fleshy,  as  in  the  tomato.  In 
others  the  outer  part  of  the  pericarp  is  hard  and  firm,  while 
the  inner  becomes  pulpy,  as  in  the  pumpkin  and  squash. 

412.  Accessory  fruits. — Parts  adjacent  to  the  carpels, 
either  flower  leaves  or  axis  or  both,  stimulated  to  growth, 
frequently  enter  into  the  formation  of 
fleshy  fruits.  These  may  be  accompanied 
by  either  a  fleshy  or  a  dry  pericarp.  In 
the  wintergreen  berry  the  calyx  grows 
thick  and  fleshy  and  surrounds  a  dry  peri- 
carp, which  cracks  at  maturity  (fig.  353). 
In  the  strawberry  (fig.  287)  the  torus  be- 
comes greatly  enlarged  and  fleshy,  while 
the  minute,  one-seeded,  dry  fruits  are 
scattered  over  its  surface,  imitating  small 
seeds.  The  fig  has  the  same  parts,  with 
the  torus  concave,  instead  of  convex  (fig. 
289).  The  apple  consists  of  a  fleshy  torus  carrying  at  its 
free  end  the  withered  calyx  and  enclosing  the  tough,  thin 


Fig.  353.  —  Fruit  of 
wintergreen  (Ga  ul- 
theria         procum- 

fie/is),  halved,  show- 
ing thin  (dry)  peri- 
carp, surrounded  by 
thickened  fleshy 
caly  x.  Magnified 
about  2  diam. — After 
Gray. 


SEXUAL    REPRl  >/'  <  'CTK  >JV 


305 


pericarp   |  fig.  354).      In   the  blackberry  the  receptacle  be- 
comes fleshy,   and   each   pistil   forms  a   minute   fruit    like  a 


Fig.  354. — Fruit  of  the  apple.     A,  halved  longitudinally; 
pericarp,  enclosing  seeds  ;  g,  vascular  bundles  of  the   tit 
calyx  leaves.     One  hall  natural  size.— After  Focke. 


alved  transversely.    /, 
torus  entering  k,  the 


cherry,  adherent  to  its  neighbors  and  to  the  pulpy  torus.  The 
raspberry  is  like  it,  except  that  the  adherent  mass  of  fruits 
separates  as  a  cap  from  a  firm  torus  (fig.  355). 

413.  Multiple  fruits.  —  If  the  flowers  form  a  crowded  in- 
florescence, either  dry  or  fleshy  fruits  may  be  closely  crowded 
at  maturity.  Under  these  conditions  fleshy  fruits  frequently 
become  adherent,  and  may  thus  constitute  a  multiple  fruit 
quite  similar  in  form  to  the  fruit   formed  by  the  aggregated 


Fig.  355 


Fig.  356. 


Fir..  3H5. — Vertical  section  of  a  flower  of  raspberry  (Rubus  idtrus),  showing  numerous 
pistils  which  form  the  caplike  fruit  over  the  enlarged  torus;  olla,  and 


calvx  all  united  .it  base.     Magnified  about  2  <li. 
Fig.  156.— A,  pistillate  flower  cluster  ol  white  1 

Natural  si/e       Alt.  i    P.aillon. 


Alter  kerne 
ilberry;  B,  multiple  fruit  from  same 


306  PLANT   LIFE. 

carpels  of  a  single  flower.  Compare  the  multiple  fruit  of  the 
mulberry  (each  section  from  a  separate  flower  whose  floral 
leaves  and  pistil  both  become  pulp}-;  fig.  356)  with  such  an 
aggregate  fruit  as  the  blackberry,  in  which  each  section  is 
one  pistil  out  of  the  many  belonging  to  a  separate  flower  (fig. 
355).      The  pineapple  is  similar  to  the  mulberry  in  origin. 

Even  more  remote  parts  are  stimulated  to  development  by 
fertilization  of  the  egg.  The  stem  bearing  the  flower  gen- 
erally grows  and  becomes  stronger,  to  carry  the  fruit,  espe- 
cially if  large.  The  minute  bractlets  sometimes  become 
highly  developed  beneath  the  fruit.  The  cup  of  the  acorn 
and  the  husk  of  the  hazelnut  originate  in  this  way  as  the 
nuts  form.  The  similar  husk  of  the  beechnut  and  chestnut 
encloses  more  than  one  fruit. 

414.  Distributive  arrangements. — Since  the  seed  plants 
abandoned  the  distribution  of  the  megaspores  and  form  both 
the  gametophyte  and  the  new  sporophyte  within  the  tissues 
of  the  old,  it  became  necessary  to  adopt  some  other  method 
whereby  the  young  can  be  so  scattered  as  to  prevent  them 
from  coming  into  sharp  competition  with  the  parents.  This 
distribution  occurs  at  the  time  of  maturity  of  the  seed,  i.e., 
when  the  embryo  has  become  dormant,  and  the  food  store 
and  protective  coverings  have  been  completed.  The  devices 
by  which  seeds  are  scattered  are  dependent  upon  the  number 
and  character  of  the  seeds  and  the  nature  of  the  pericarp. 
Thus,  one-seeded,  indehiscent  fruits  must  be  scattered  by  the 
structures  arising  upon  the  surface  of  the  pericarp  or  its  ad- 
herent parts.  On  the  contrary,  seeds  which  escape  from  the 
pericarp  have  the  distributive  structures  developed  by  the 
seed  coats  themselves.  For  distribution  plants  adapt  them- 
selves so  as  to  employ  the  agency  of  the  wind,  water,  and 
animals,  or  they  develop  special  mechanisms  for  casting  off 
the  seed  as  a  projectile.  A  consideration  of  these  adapta- 
tions belongs  to  ecology.      (See  Chap.   XXVI.) 


PART   IV:   ECOLOGY. 

415.  Definition. — Physiology,  in  its  broadest  sense,  may 
be  divided  into  physiology  proper  and  ecology.  Ecology 
is  that  portion  of  botanical  science  which  treats  of  the  rela- 
tions of  the  plant  to  the  forces  and  beings  of  the  world  about 
it,  as  distinguished  from  physiology  proper,  which  treats 
of  the  relation  of  the  plant  as  a  whole  to  the  chemical  and 
physical  forces  within  it.  The  forces  without  the  plant 
necessarily  limit  and  modify  the  action  of  the  forces  within 
it;  consequently  it  is  quite  impossible  to  draw  a  sharp  dis- 
tinction between  those  subjects  which  belong  to  ecology  and 
those  which  belong  to  physiology  proper.  Parts  II  and  IV, 
therefore,  will  be  found  to  overlap  in  many  places.  Several 
of  the  subjects  already  treated  under  physiology  belong  in 
part  to  the  present  section.  for  example,  the  movements 
of  plants  are  due  not  to  internal  causes  alone,  but  to  internal 
causes  as  modified  by  external  conditions.  In  this  part  only 
a  bare  outline  of  the  adaptations  of  plants  in  form  and  habit 
to  their  physical  surroundings  and  to  other  living  beings  i  an 
be  given. 

307 


I.  NUTRITIVE   ADAPTATIONS, 

|  I.     ADAPTATIONS  OF  FORM  AND  STRUCTURE 
TO  ENVIRONMENT. 

CHAPTER  XIX. 

FORMS  OF  VEGETATION. 

416.  Adaptation. — The  various  physical  conditions  which 
make  up  the  "climate"  of  any  particular  region  of  the 
earth's  surface,  together  with  the  nature  of  the  substratum 
upon  or  in  which  the  plant  grows,  largely  control  the  form 
and  functions  of  the  plants  found  in  that  region.  Stated  in 
other  words,  plants,  in  order  to  exist  at  all,  are  compelled  to 
adapt  themselves  to  the  places  in  which  they  grow.  This 
compulsion  is  on  pain  of  death. 

417.  The  struggle  for  existence. — The  competition  be- 
tween plants  is  intense.  Only  a  very  small  portion  of  the 
seedlings  which  start  in  any  particular  area  can  come  to 
maturity.  Far  the  greater  number  will  be  killed  by  being 
robbed  of  light  and  of  water  by  the  overshadowing  leaves 
and  interlacing  roots  of  their  companions.  Since  such  com- 
petition exists,  it  is  evident  that  only  those  best  suited  to  the 
conditions  under  which  they 'grow  will  have  any  chance 
whatever  to  survive. 

Not  only  are  individuals  subject  to  this  competition,  but 
all  individuals  of  a  particular  kind  (a  species)  may  be  de- 
stroyed in  any  region  through  the  competition  of  other 
species    better    suited     to    the    conditions     of    that    region. 


FORMS    OF    VEGETATION.  309 

Through  this  competition  between  species  one  kind  may  be 
forced  to  migrate  to  some  different  region  in  order  to  main- 
tain itself.  The  capacity  of  a  plant  to  adapt  itself  to  a  differ- 
ent environment  determines  the  possibility  of  its  occupying 
a  new  region,  for  here  it  must  come  into  competition  with 
other  sorts,  and  can  only  maintain  itself  if  it  is  capable  of  so 
modifying  its  form  and  structure  as  to  adapt  them  to  the  new 
conditions,  and  that  as  well  as  or  better  than  the  occupants 
it  finds  in  possession.  In  the  beginning  it  was  probably  by 
competition  between  species  that  water  plants  were  gradually 
adapted  to  an  amphibious  life,  and  then  to  a  terrestrial  life, 
all  the  while  advancing  in  complexity;  later  some  green 
plants  adapted  themselves  to  a  parasitic  or  saprophytic  life ; 
plants  of  moist  regions  gradually  moved  out  and  occupied 
even  the  deserts  ;  plants  loving  the  shade  adapted  themselves 
to  the  direct  light  of  the  sun  ;  and  so  on,  until  all  parts  of 
the  earth's  surface  and  even  considerable  depths  of  the  ocean 
have  been  occupied. 

418.  Environment.— In  order  to  understand  the  variety 
of  factors  which  are  acting  upon  any  particular  plant,  it  will 
be  instructive  to  consider  the  conditions  which  surround  the 
ordinary  land  plant.  A  portion  of  such  a  plant  is  imbedded 
in  the  soil,  and  the  remainder  rises  into  the  air.  The  sub- 
terranean part  is  profoundly  influenced  by  the  size  and  form 
of  the  soil  particles,  as  well  as  by  their  chemical  composition. 
It  is  exposed  to  contact  with  water  varying  in  amount,  some- 
times from  day  to  day  and  always  from  time  to  time  during 
the  year,  holding  many  substances  in  solution  in  varying 
amounts  and  kinds  at  different  periods.  It  is  subject,  also, 
to  variations  of  temperature  from  day  to  day  and  from  season 
to  season. 

The  aerial  part  of  such  a  plant  is  exposed  to  greater  or 
less  variations  of  temperature  from  hour  to  hour,  from  day 
to  night,  from  day  to  day,  and  from  season   to  season.      It  is 


3IO  PLANT  LIFE. 

exposed  to  light  varying  in  intensity  from  day  to  night  and 
from  day  to  day,  and  to  light  differing  in  direction  from  hour 
to  hour  of  each  day.  It  is  enveloped  by  fogs  or  mists,  or  is 
pelted  by  rain,  hail,  sleet,  or  snow,  and  sometimes  com- 
pletely buried  in  ice  or  snow. 

A  plant  has  little  or  no  power  to  alter  any  of  the  agents 
which  act  upon  it,  but  it  must  be  able  to  withstand  the  in- 
jurious ones,  or  even  to  turn  them  to  its  advantage.  It 
would  be  difficult  to  conceive  a  more  complex  set  of  factors 
to  which  adjustment  must  be  effected  ;  and  the  more  since 
these  conditions  are  combined  with  each  other  in  an  infinite 
variety  of  ways.  Because  the  physical  conditions  vary  in 
different  parts  of  the  earth's  surface,  the  vegetation  in  each 
region  differs  from  that  in  others. 

In  any  particular  locality  certain  conditions  of  water,  soil, 
air,  temperature,  light,  and  precipitation  are  likely  to  be  as- 
sociated. It  is  possible,  in  a  somewhat  arbitrary  way,  to 
recognize  four  general  sets  of  conditions  to  which  plants  must 
adapt  themselves,  in  each  of  which  the  water  supply  is  the 
predominant  factor.  It  should  be  understood  clearly,  how- 
ever, that  these  sets  of  conditions  pass  into  each  other  im- 
perceptibly. Corresponding  to  these  four  sets  of  external 
conditions,  we  may  recognize  certain  characteristics  in  plant 
form  and  structure,  which  are  likely  to  be  as>ociated,  and  it 
thus  becomes  possible  to  distinguish  four  forms  of  vegetation 
corresponding  to  the  four  sets  of  external  conditions. 

419.  The  first  set  of  conditions  consists  of  those  charac- 
terized by  no  extremes.  Both  the  air  and  the  soil  are  moder- 
ately moist;  the  precipitation  is  distributed  through  the 
year,  or  at  least  through  the  growing  season  ;  there  is  no  ex- 
cess of  salts  in  the  water  or  in  the  soil  ;  the  soil  is  usually 
enriched  with  organic  matter,  often  in  considerable  amount. 
The  plants  which  grow  under  these  conditions  are  the  ones 
most  familiar  to  people  in  the  fertile  regions  of  temperate 


FORMS    OF   VEGETATION.  311 

climates.     These  may  be  reckoned  as  the  average,  or  mean, 
plants,  and  are  therefore  called  technically  mesophytes. 

420.  A  second  set  of  conditions  is  characterized  by  de- 
ficient water  supply  throughout  the  year,  the  amount  of  water 
present  in  the  soil  often  being  less  than  10$.  Such  regions 
may  be  considered  as  regions  of  continuous  drought.  The 
plants  adapted  to  these  conditions  are  known  as  drought 
plants,  or  xerophytes. 

421.  A  third  set  of  conditions,  prevailing  over  compara- 
tively limited  regions,  is  characterized  by  an  excess  of  salts  in 
Ike  soil  or  water.  These  salts  are  chiefly  sodium  chloride 
(NaCl,  common  salt),  gypsum  (CaSOj,  and  magnesium 
chloride  (MgCl).  Plants  which  can  live  under  these  condi- 
tions are  known  as  salt  plants,  or  halophytes. 

422.  A  fourth  set  of  conditions  is  characterized  by  an 
excess  of  water.  The  plants  grow  wholly  or  partly  surrounded 
by  water,  or  their  roots  are  imbedded  in  a  soil  supersaturated 
with  water,  that  is,  containing  at  least  8o$.  Such  plants  are 
called  water  plants,  or  hydrophytes. 

It  will  be  noticed  that  the  first  three  groups,  namely,  meso- 
phytes, xerophytes,  and  halophytes,  are  essentially  land  plants 
in  distinction  from  the  fourth  group,  which  are  water  plants. 


CHAPTER  XX. 

MESOPHYTES. 

423.  I.  Mesophytes  show  certain  general  relations  to  ex- 
ternal conditions,  many  of  which  are  also  shared  by  other 
forms.  Except  to  these  minor  variations  in  the  environment, 
they  show  no  special  adaptations  ;  or,  rather,  they  are  looked 
upon  as  the  normal  plants,  and  the  ways  in  which  others 
differ  from  them  are  spoken  of  as  special  adaptations.  In 
reality,  however,  the  general  methods  by  which  they  adapt 
themselves  to  their  environment,  which  are  now  to  be  con- 
sidered, are  quite  as  much  special  adaptations  as  those  shown 
by  plants  living  in  extreme  climates.  These  adaptations  will 
be  discussed  in  relation  to  each  of  the  main  factors  of  the 
environment. 

424.  i.  Air. — The  composition  of  the  air  varies  little  from 
place  to  place.  It  is  only  in  those  regions  in  which  it  is 
rendered  impure  by  artificial  means,  such  as  the  vicinity  of 
cities  and  factories,  and  in  the  few  isolated  regions  in  which 
it  is  vitiated  by  natural  means,  as  in  volcanic  regions,  that 
any  special  adjustments  may  be  looked  for.  Artificial  vitia- 
tion of  the  air  kills  off  certain  plants.  A  few  plants  have 
adapted  themselves  to  air  in  the  neighborhood  of  fumaroles, 
where  they  are  subjected  to  vapors  containing  large  amounts 
of  sulphurous  acid.  Whatever  special  adaptations  are  found 
are  internal,  since  only  the  very  simplest  plants  find  it  pos- 
sible to  live  in  such  conditions. 

The  movements  of  die  air,  however,  influence  profoundly 

312 


MESOPHYTES.  313 

the  form  of  plants.  This  they  do  indirectly  by  the  shifting 
of  sands  in  sandy  regions,  and  by  their  effect  upon  the  pre- 
cipitation and  upon  the  moisture  of  the  atmosphere.  Winds 
increase  evaporation  from  the  soil  and  from  the  surface  of 
plants,  and  thus  directly  influence  form.  Trees  growing  in 
wind-swept  regions  are  always  low,  bushy-branched,  with 
the  trunk  and  limbs  inclined  to  leeward.  The  twigs  on  the 
windward  side  are  often  dead.  Forests  in  wind-swept  regions 
often  thin  out  to  windward,  the  trees  becoming  smaller  and 
smaller,  finally  being  replaced  by  bushes  which  become 
sparser  until  no  woody  vegetation  is  present.  The  leaves 
upon  such  plants  are  small  and  often  peculiarly  spotted. 
These  effects  upon  the  form  have  been  ascribed  to  the  me- 
chanical action  of  the  air,  to  the  presence  of  salts  when  in  the 
neighborhood  of  the  ocean  or  salt  lakes,  and  to  the  reduced 
temperature ;  but  probably  none  of  these  causes  is  to  be 
looked  upon  as  so  efficient  as  the  drying  brought  about  by 
the  prevalent  wind. 

425.  2.  Light. — Light  affects  plants  directly  through  its 
influence  upon  their  nutrition  and  upon  the  evaporation  of 
water  from  their  surfaces.  In  this  way  it  affects  (1)  the  rate 
of  development.  For  example,  the  blossoming  of  flowers 
and  the  production  of  leaves  occur  earlier  upon  the  sunward 
side  of  a  tree  or  shrub  than  upon  the  other  side.  In  the 
same  cultivated  crops  of  the  north  and  south  there  will  often 
be  several  days'  difference  in  the  total  number  between  sow- 
ing and  maturing.  Thus  barley  at  northern  Norway,  in  68°  N. 
lat.,  matures  in  89  days,  while  at  Schonen,  in  560  N.  lat.,  it 
matures  in  100  days.  Since  the  total  hours  of  illumination 
must  be  about  equal,  the  longer  days  of  the  north  enable  the 
plants  to  produce  more  food,  and  so  to  mature  more  rapidly. 
The  forcing  of  vegetables  under  glass  by  the  aid  of  electric  light 
during  the  night  depends  upon  the  same  principle.  (2)  The 
form  of  plant  parts  is  directly  influenced  by  light.    Plants  accus- 


314      J  PLANT  LIFE. 

tomed  to  the  direct  sunlight  and  those  accustomed  to  shad-' 
show  profound  differences  in  habit.  Light  plants  are  stocky  and 
compact ;  their  stems  are  inclined  to  be  woody,  the  leaves 
are  usually  folded  or  crisped  aud  often  set  at  an  acute  angle 
with  the  direction  of  the  light,  and  the  surfaces  are  frequently 
hairy.  In  contrast,  shade  plants  are  slender  and  sprawling; 
their  stems  often  thin  and  weak  ;  the  leaves  flat  and  smooth 
and  set  transverse  to  the  direction  of  the  light-rays,  while  the 
surface  is  slightly,  if  at  all,  hairy.  (3)  In  internal  structure ; 
,-ajso,  there  are  decided  differences,  particularly!!!  the  lea  ves. 
(See  %"  167,  438.)  The  leaves  of  light  plants  usually  have  a 
thick  epidermis,  often  shiny,  with  lateral  walls  straight  ;  the 
stomata  are  frequently  confined  to  the  under  side  and  often 
,sunk;   the   palisade   cells   are  elongated,  sometimes   forming 

(two  or  three  layers  and  occasionally  appearing  on  both  faces 
of  the  leaf.  The  shade  plants,  on  the  contrary,  have  a  thin 
epidermis,  often  containing  chlorophyll,  with  lateral  walls 
often  very  wavy  ;  the  stomata  are  produced  on  both  sides  of 
the  leaves,  and  the  palisade  tissues  are  poorly  developed. 
Light  plants  frequently  have  red  cell-sap,  especially  in  the 
epidermis  of  smooth  plants,  and  their  colors  are  always 
deeper,  especially  in  the  plants  of  high  latitudes.  Shade 
plants,  on  the  other  hand,  are  usually  pale,  rarely  high- 
colored. 

426.  3.  Temperature. — Temperature  exercises  an  im- 
portant influence  upon  plants,  both  upon  their  aerial  and  sub- 
terranean parts.  The  temperature  of  the  air  is  really  much 
more  important  in  controlling  the  adaptations,  and  con- 
sequently the  geographic  distribution,  of  plants  than  is  light. 
The  reason  for  this  is  to  be  found  in  the  much  more  unequal 
distribution  of  temperature  in  various  regions  of  the  earth's 
surface.  Moreover,  temperature'  affects  every  vital  function 
of  the  plant,  for  each  of  which  a  maximum,  minimum,  and 
optimum  point  maybe  determined.     (See  ^[  186,  263.)     The 


MESOPHYTES.  3^ 

variations  in  temperature  to  which  plants  are  subjected  require 
special  adaptations. 

427.  (a)  Protection  against  changes  of  temperature. — 
These  adaptations  arc  to  be  found  in  the  presence  of  special 
cell-contents,  such  as  oils  or  resins,  which  reduce  the  liability 
of  those  cells  to  freezing  ;  in  the  reduction  of  the  amount  of 
water  in  cells  so  that  less  damage  results  from  freezing  ;  and, 
finally,  in  the  presence  of  poor  conductors  of  heat,  such  as 
scale-leaves  and  hairs  in  profusion,  a  jacket  of  old  withered 
leaves,  etc.,  all  of  which  insure  slow  thawing  if  the  plant  is 
frozen.  The  winter  buds  of  trees  in  temperate  climates 
illustrate  all  of  these  adaptations. 

428.  (l>)  A  dormant  period  is  necessitated  by  low  tem- 
perature during  part  of  the  year  in  temperate  and  arctic  cli- 
mates. The  period  of  vegetation  in  the  higher  latitudes  is 
often  very  short.  The  same  conditions  prevail  at  high  alti- 
tudes, with  the  same  effects.  In  these  regions,  therefore,  the 
plants  are  almost  all  perennials.  In  many  cases  the  rudiments 
of  flowers  are  formed  in  the  year  preceding  that  in  which 
they  are  developed,  in  order  that  full  opportunity  may  be 
given  for  the  ripening  of  the  seeds  and  fruits  in  the  short 
growing  season.  Some  plants  adapt  themselves  to  short 
periods  of  vegetation  by  the  presence  of  evergreen  leaves, 
which  are  ready  at  the  first  opportunity  to  resume  their  work 
of  food  manufacture. 

429.  ( c )  The  form  of  plants  is  modified  by  the  tem- 
perature of  the  air  and  soil.  Tow  temperatures  are  also 
likely  to  bring  about  the  formation  of  dwarf  plants. 

430.  (d  The  rate  of  development  is  strikingly  influenced 
by  variations  in  the  temperature  of  the  soil.  The  soil  heat  is 
derived  from  the  sun  and  from  the  decomposition  of  organic 
matter  within  it.  The  sun  is  far  the  most  important  source. 
The  amount  of  lnat  absorbed  varies  with  the  exposure  of  the 
soil,  its  color,  porosity,  amount  of  water,  and  the  duration  of 


3I<3  PLANT  LIFE. 

the  sun's  rays.     The  influence  of  the  temperature  of  the  soil 

is  mainly  indirect,  acting  through  its  effect  on  the  water 
supply  of  the  plant. 

431.  (c)  Moisture  and  precipitation. — The  amount  of 
moisture  in  the  atmosphere  largely  determines  the  amount  of 
evaporation  from  the  surface  of  the  plant.  The  relative 
amount  of  moisture  in  the  atmosphere  is  exceedingly  variable, 
and  bears  a  direct  relation  to  its  temperature.  Indeed,  so 
closely  related  are  the  conditions  of  temperature,  light,  and 
moisture  in  the  air,  that  the  adaptations  of  shade  plants, 
mentioned  above,  may  be  considered  as  the  sum  of  the 
effects  due  to  these  three  factors.  It  is  difficult,  if  not  im- 
possible at  present,  to  say  which  are  the  effects  of  light  and 
which  of  evaporation. 

Precipitation  affects  plants  chiefly  as  it  influences  water 
supply.  A  few  plants  only  of  the  higher  forms  are  able  to 
absorb  moisture  directly  from  the  air,  except  as  a  last  resort. 
(See  %  196.)  Many  of  the  lower  plants,  such  as  the  algae, 
lichens,  and  mosses,  absorb  rain  instantly  by  their  aerial 
parts.  Some  plants  have  adapted  themselves  to  frequent  and 
prolonged  rainfall,  bearing  it  often  for  months  at  a  time  ; 
other  plants  under  such  conditions  lose  their  leaves  very 
quickly.  Rain-loving  plants  have  their  leaves  furnished  with 
elongated  tips  or  with  grooves  and  hairs  to  carry  off  the  rain 
quickly.  Their  surfaces,  also,  are  not  readily  wetted  by  water. 
Others  protect  themselves  against  the  rain  by  adjusting  the 
direction  of  their  leaves  to  it  so  that  a  heavy,  splashing  rain 
strikes  them  at  an  acute  angle.  Others,  by  a  movement  of 
their  leaves  as  soon  as  the  sky  is  clouded,  avoid  injury  from 
heavy  rains.  The  branching  of  leaves  in  certain  cases  may 
be  looked  upon  as  a  protection  against  heavy  rainfall. 

The  snow  cover  through  cold  periods  is  for  many  plants 
essential  as  a  protection  against  low  temperatures  during  the 
dormant  period.     Others  have  adapted  themselves  to  growing 


MESOPHYTES.  3'7 

even  in  the  midst  of  snow,  putting  forth  their  leaves  and 
blossoms  while  still  surrounded  by  melting  snow. 

432.  ( /')  Soil.  —  Both  the  chemical  composition  and  the 
physical  properties  of  the  soil  affect  plants.  The  latter  arc, 
however,  by  far  the  most  important.  Here,  again,  the  reason 
is  to  be  found  in  the  relation  of  the  physical  qualities  of  soil 
to  the  water  supply. 

The  water  which  permeates  the  soil  takes  up  from  it  certain 
substances,  and  becomes  thus  a  dilute  solution  of  various 
salts.  That  the  salts  thus  present  in  the  soil  water  may  affect 
the  form  of  the  plant  is  strikingly  shown  in  the  occurrence 
of  certain  species  of  a  genus  only  upon  soils  containing  lime, 
while  others  of  the  same  genus  are  found  only  in  soils  free 
from  lime.  When  the  local  distribution  of  corresponding 
species  of  the  same  genus  within  the  same  region  is  deter- 
mined by  the  presence  or  absence  of  lime  in  the  soil,  com- 
parison of  them  indicates  the  general  effect  of  lime  salts  upon 
the  plant.  Plants  growing  upon  lime  are  usually  stronger 
and  more  densely  hairy,  often  hoary,  while  those  on  other 
soils  are  smooth  or  furnished  with  glandular  hairs.  The 
lime-loving  plants  have  bluish-green  leaves,  as  contrasted 
with  the  grass-green.  Their  leaves  are  also  more  numerous 
and  more  deeply  branched,  the  flowers  larger  and  their  colors 
dulkr  and  paler. 


CHAPTER  XXI. 

XEROPHYTES  AND  HALOPHYTES. 

433.  II.  Xerophytes. — The  plants  of  dry  regions  blend 
by  imperceptible  gradations  with  the  mesophytes.  They 
reach  their  best  development  in  desert  and  rocky  regions. 
Some,  especially  of  the  lower  forms,  grow  in  such  situations 
that  they  must  adapt  themselves  to  become  so  dry  at  certain 
periods  that  they  may  be  powdered.  Such,  for  example,  are 
a  few  algae,  many  lichens,  mosses,  and  a  few  fernworts. 
Adaptations  in  these  cases  must  be  looked  for  in  the  character 
of  the  cell  contents. 

Other  plants  must  adapt  themselves  to  endure  dry  periods, 
such  as  those  occurring  from  day  to  day,  or  between  the  wet 
and  dry  seasons,  by  retaining  in  their  bodies  sufficient  water 
to  sustain  life.  The  following  are  some  of  the  chief  methods 
by  which  plants  adapt  themselves  to  periodic  or  continuous 
drought. 

A.    Adaptations  for  reducing  transpiration. 


434.  i.  Periodic  reduction  of  surface  exposed. — -The 
dying  away  of  an  annual  plant  after  forming  its  seed  may  be 
looked  upon  as  an  adaptation  of  this  sort.  Little  evaporation 
occurs  from  the  surface  of  the  seed,  which  is  thus  adapted  to 
withstand  prolonged  dryness.  Perennial  plants  accomplish 
the  same  results  when  their  annual  shoots  die  off  and  leave 
only  the  rhizomes,  tubers,  and  similar  parts  buried  in  the  soil. 
Perennial  plants  with  perennial  shoots  may  drop  their  leaves 

318 


XEROPHYTES  AND    HALOPHYTES.  319 

during  the  dry  period  and  form  them  again  upon  the  return 
of  the  growing  season.  The  fall  of  leaves  in  our  woody  vege- 
tation is  a  similar  adaptation  to  the  cold  season.  The  rolling 
or  curling  of  leaves  is  a  common  mode  of  avoiding  evapora- 
tion.     It  is  common  in  grasses  (  fig.  357)  and  mosses. 

435.    2.   The    constant    reduc- 
tion  of    exposed    surface. — This 
B  ^fl^  may  be  secured  among  the  leaves 

by    reducing  them  either   in  area 
f  or  in  number  or  both,  or  by  much 
ranching,  with  little  green  tissue 

A 
Fig.  357. — Transverse  sections  of  a  gra>-s  leaf  (Lasiagrostis).  .1,  open;  A',  rolled, 
when  dry.  The  white  plates  are  the  ribs  of  mechanical  tissue  above  and  below  a 
stele,  one  in  each  ridge  ;  the  shaded  areas  are  green  tissue.  The  Stomata  are  located 
low  on  the  sides  of  the  narrow  grooves  between  the  ridges,  so  that  when  the  leaf  is 
rolled,  evaporation  through  them  is  hindered.     Magnified  16  diam. — After  Kerner. 

Plants  with  bristje-shnpr-'1  "'■  "—die-shaped  leaves  (tigs.  10 1, 
358),  those  with  permanently  rolled  leaves  (fig.  359),  or 
those  with  scale-like  leaves  I  fig.  100  )  show  thevarious  phases 

of  such  adaptations^ KxtrenuT reduction  oTsurface  is  secured 

by  suppression  of  leaves.  In  this  case  any  further  adaptation 
depends  upon  the  stems,  which  must  also  provide  fornutritive 
work.  The.se  may  take  the  form  of  leaves  1  see  €  112); 
or  the  branches  may  be  thick,  rigid,  and  fleshy  1  fig.  360)  ; 
or  they  may  be  thread-like  or  needle-shaped,  as  in  the  aspara- 
gus (fig.  105)  ;  or  the  stems  themselves  may  reduce  their  area 
by  becoming  fleshy  and  cylindrical,  prismatic,  or  spheroidal, 
as  in  the  various  forms  of  Cereus  and  melon  <a<tuses  (fig. 
1 10). 

436.  3.  Movements  of  parts  to  reduce  the  illumina- 
tion.— Certain  lea\es  are  adapted  to  a  permanent  profile 
position,    that    is,    with    the    edges    turned    toward    the    sky. 


320 


PLANT  LIFE. 


instead  of  the  surfaces.  (See  ^|  285.)  Others  assume  a 
profile  position  when  the  illu- 
mination becomes  too  intense. 
These  positions,  by  placing  the 
leaf  surface  oblique  to  the  di- 
rection of  the  light  rays,  reduce 
the  amount  of  evaporation  very 
considerably. 

437.  4  Coverings,  consist- 
ing of  living  or  dead  scale- 
leaves,  stipules,  leaf-bases  or 
entire  leaves,  reduce  transpira- 
tion by  obstructing  the  free  ex- 
change of  air,  or  by  holding 
water  and  so  keeping  moist  the 
surfaces  they  cover. 

438.  5.  Structural  modifi- 
cations. — ■  These  may  occur 
either  in  the  epidermis- or  some 
internal  tissues.  (a)  The  epi- 
dermis may  greatly  reduce  evap- 
oration by  the  formation  of 
hairs  in  such  profusion  as  to 
form  a  cover  for  the  surface 
(figs.  361-364).  Hairs  in- 
tended to  protect  from  evap- 
oration   are    usually    dead  and 

filled  with  air.  Reflecting  light  from  many  points,  they  look 
white,  and  the  surface  seems  hoary,  or  woolly,  or  silky. 
Hairs  in  the  form  of  scales  which  overlap  reduce  the  rate  of 
evaporation  by  covering  the  stomata  (fig.  365).  -Iuirther__ 
adaptations~ot  the  epidermis  are  to  be  found  in  the  pres- 
ence of  a  thick  cuticle  (fig.  367);  the  water-proofing  of 
the  whole  of4he  outer  wall  of  the  epidermis;  the  develop- 


.  —  Shoot  of  larch,  with  ripe 
showing  needle-shaped  leaves 
on  dwarf  branches ;  scale  leaves  on 
main  axis  ;  carpellary  scales  just  peep- 
ing from  between  placental  scales  of 
cone.     Natural  size. — After  Ke 


XEROPHYTES   AND    HA  l.OPH  YTES. 


321 


ment  of  two  or  more  layers  of  epidermal  cells  (fig.  370)  ;    or 
the  excretion  of  wax  or  of  varii+*ff  upon  the  surface  of  the  epi- 


FTOXrs: 


Fig.  359. — Transverse  section  of  a  leaf  of  a  heath  {Tylanthus  ericoides),  showing 
revolute  form.  The  stomata  are  on  the  under  (concave)  surface  among  the  hairs, 
winch  still  further  impede  the  transpiration.     Magnified  130  diam. — After  Kerner. 


dermis.     The  latter  often  becomes  very  thick,  giving  to  the 
leaves  a  shiny  appearance.      Wax  is  usually  in  the  form  of  a 


Fig.  36 


Fig.    360. — Prickly    pear    (  >puntia    vulgaris)  with    Battened  jointed   stem   and   no 

leaves.    About  one  fourth  natural  size,     After  Frank, 
Fu;.  361.— Multicellular  hairs  ol  edelweiss,     MagnifU  d  about  50  diam.— After  Kerner, 
Fir..  362. — Silky  unicellular  hairs  ol   Convolvulus  Cntorum.     Magnified  about   $" 

ili.1111        Ml.  1    K(  ii"  1 


322 


PLANT    LIFE. 


--:' :\  ' 


bluish-white  powder,  which  can  be  readily  wiped  off  with  the 

ringers,  as  from  the  surface 
of  fruits,  such  as   plums  or 
grapes,    the   leaf  of    cab- 
bage, or  the  stalk  of  sugar- 
cane  (fig.  366).      The   in- 
^     terior  layers  of  the  wall  6T 
■    the  epidermis    are   some- 
- — ttmeT'coivverted  into  rhu- 
~~cTTage,  which    retards    the 
evaporation     ~rjf — -avuU£.i\__ 
^J£he__sinking    of"  the    sto- 
mata    below     the     general 


Fig.  363. 


wr 


Fig.  363.-  Stellate  hairs  <>f  /h<i/:i 
Thomasii,  seen  from  above. 
Magnified   about    50    <li. 

After  kerner. 

Fig.  364. — T-shaped  hairs  of  Ar- 
temisia mutellina.  Magnified 
about  50  diam.— After  Kerner. 

1, .  565  Shieldlike  si  .<l<--s  of  an 
1   1  /■:/,., ix  "'>■■■  ■• 

folia),  seen  from  above.  Mag- 
nified about  ;•>  diam.— After 
Kerner. 


level  (fig.  367),  their  arrangement  in  pits  (fig.  368)  or  in 
"groTTves  (fig.  357),  and  their  restriction  to  the  under  side  of 
the  leaf  (fig.  359)  may  be  looked   upon  as  further  epidermal 


XEROPHYTES   AND    HALOPHYTES. 


323 


,ni1-ipfntjnnc    tp    r^dll^w^yapnrririrm  In    the    leaVCS    of   SOUK' 

xerophytes  the  guard  cells  of  the  stomata  are  motile  only 
when  young,  becoming  thick-walled  and  fixed  when  the  leaf 
is  mature.      The  stoma  itself  sometimes  becomes  closed,  also. 


Fig.  366.-  -Portion  of  a  transverse  section  through  a  node  of  sugar-cane,  showing  rods 
of  wax  secreted  by  the  epidermis.     Magnified  142  diam.— After  I  »e  Bary. 

FlG.  367. — Transverse  section  of  a  portion  of  the  margin  of  a  leaf  of  Aloe  socotrina. 
1.  thick  cuticle;  below,,  cutinized  layers  of  wall  of  epidermis,*'/;  /,  parenchyma 
cells  with  chloroplasts  ;    .  r.  a  crystal  cell  with  needle  crystals  ot   oxalate  of  lime;  sp, 

fuard  cells  of  stoma,  sunk  below  surface  :  .;,  intercellular  space  under  stoma.    Magni- 
ed  about  175  diam. — After  Tschirch. 


_{&L-l'he  internal  tissues  ofthe  leaves  may  be  more  compact. 
This  reduces  transpirationby  restricting  thelil'ea  of  llie-air 
passages.  Such  dense  structure  is  secured  by  multiplying 
the  number  of  the  palisaTrrriTTycrs  and  by  the  "Tub  re  regular 
form  of  the  spongy  parenchyma  (fig.  359  and  ^'  167). 


B.   Adaptations  for  taking  up  water. 

439.  Absorption. —  1.  Some  plants  are  adapted  to  im- 
mediate absorption  of  moisture  in  the  air  or  of  liquid  water 
falling  en  their  aerial  parts.  Such  are.  usually,  the 
algae,  In  hens,  and  mosses  which  -row  in  exposed  situations. 
2.  Certain  of  the  higher  plants  are  furnished  with  hairs 
adapted  to  the  prompl  absorption  of  rain  or  dew,  e.g.,  Spanish 


324 


PLANT   LIFE. 


moss.      3.   <  Uhcr  plants  adapt  aerial  routs  to  the  absorption  of 

moisture  from  the  air,  as  well  as  falling  water.  (See  ^  196.) 
4.  Many  are  surrounded  by  the  bases  of  dead  leaves,  which 
act  as  a  sponge  for  absorbing  water,  and  supply  it  gradually 
to  the  stem  or  younger  leaves.  Living  leaves,  sometimes 
singly,  sometimes  in  clusters,  form  cuplike  or  tubular  struc- 


Fk;.  368.— Portion  of  a  vertical  section  of  leaf  of  oleander.  <■/,  epidermis  of  upper 
face;  e/>' ,  same  of  lower  face  with  stomata,  s,  in  deep  pits  with  numerous  hairs,  t: 
pal,  palisade  parenchyma  in  two  layers;  ,r/,  spongy  parenchyma;  //,  /;',  hypoderma 
adapted  to  water  storage.  Chloroplasts  shown  only  in  left-hand  side  of  figure. 
Magnified  about  175  diani.  — After  Van  Tieghem. 

tures,  acting  as  water  receptacles,  from  which  it  can  be 
absorbed  as  required.  Such  adaptations  occur  chiefly  in 
epiphytes.  (See"  454-)  5-  Many  xerophytes  develop  ex- 
ceedingly long  tap  roots,  which  penetrate  the  soil  deeply 
to  a  permanent  water  supply. 


XEROPHYTES   AND    HALOPH YTES.  325 

C.  Adaptations  for  storing  water. 

440.  1 .  Special  cell  contents. — The  simplest  of  these  adap- 
tations is  the  presence  of  mucilage  in  the  cells,  arising  from 
the  cell-wall  or  developed  in  the  cell-sap  of  various  parts. 
(See  *j"  5.)  The  presence  of  acids,  tannins,  and  salts  perhaps 
aids  in  the  retention  of  water. 

441.  2.  Water-storing  tissues. — (a)  Fleshy  plants,  or 
succulents,  are  those  which  thicken  their  parts  by  the  develop- 
ment of  an  unusual  amount  of  parenchyma,  which  contains 
a  large  quantity  of  cell-sap,  and  usually  much  mucilage. 
These  thin-walled,  mucilage-containing  tissues  form  a  reser- 
voir for  the  storing  of  water.  In  such  plants  the  epidermis 
is  very  strongly  water-proofed;  the  stems  are  thick,  cylin- 
drical, prismatic  or  spheroidal  ;  the  leaves  are  wanting,  or  they 
are  thick  and  fleshy,  cylindrical  or  broad  (fig.  369),  and 
arranged  in  rosettes. 

(U)  In  non-succulents, 
the  epidermis  itself  may 
be  greatly  developed  as 
a  water-storing  tissue, 
or  it  may  form  great 
numbers  of  bladdery 
hairs  which   are    richly 

supplied  with  water,  as    FlG,  3,9._A  3Trfto«£k  \sL* 
in  the  well-known  "ice-      ^SVSSSPfoKS  5*?e3KF 

,i„„,    ••       ._    ,,.i,;,.k     ,k.,        branches,      these  become  detached  and  form  in- 
piam,         on    \\nun     lilt,        dependent  plants.     About  one  half  natural  size.— 

hairs  glisten  like  ice.  After  Gray. 

In  the  first  case,  the  epidermis,  instead  of  forming  a  single 
layer  of  cells,  ma)  develop  into  several  layers,  the  lower  ones 
large  and  thin-walled,  as  in  begonias,  figs,  and  peppers  I  fig. 
370).  The  cells  immediately  under  the  epidermis  sometimes 
become  transformed  into  a  water-storing  tissue,  as  in  the 
oleanders  (fig.  368);    or  strips  of  tissue  extending  from  the 


326 


PLANT  J.ll-F. 


upper    to   the   lower  side   of   the  leaf  may  act  as  reservoirs 

of  water. 

442.  3.  Tubers  and  bulbs. —  These  forms  of  the  shoot 
in  which  the  parenchyma  is 
abundant  and  richly  supplied 
with  water  may  also  be 
counted,  in  part  at  least,  as  an 
adaptation  for  water-storage. 
443.  III.  Halophytes.  — 
The  salt-loving  plants  arc, 
in  most  of  their  characters, 
strikingly  similar  to  the  xero- 
phytes.  This  similarity  is  to 
be  explained  probably  by  the 
difficulty  of  securing  a  suita- 
ble water  supply.  They  grow 
near  the  ocean,  upon  the 
shores  of  salt  lakes,  by  salt 
springs,  and  in  the  interior 
of  the  great  continents  in  old 
lake  basins  in  which  the  salts 
have  accumulated  by  the 
rains.  A  few  of  the  halophytes 
are  trees  and  shrubs,  with 
leathery  leaves,  but  almost  all 
are  succulents.      In  habit  thev 


Fig  370.  — Strip  from  a  vertical  section  of 
leal  "I  Peperomia  trichocarpa.  ./,  from 
afreshleaf;   w,  water-storing  tissue,  com-  ov»n*»rallv  In™    nft*»n  ,-.-,.,>  1, 

posed    of    the    multiple    epidermis    of    the  arC  ,^lUiall\    IOW,  otUll  (  Ucp- 

upper  side  ;*,  chlorophyll-bearing  cells;  •  j,       (jj    ,         fl     «  ■,,,(! 

s,  spongy  parenchyma  with  sparse  chloro-  "J6»     "ll"     nnii\,     iksiij      aiiu 

plastS  and  much  water.      /.'.  tin-  same  after  ____,    _,  1    ,     .  #.___  ,1,,   .   ,„f  1  ^„,.    c. 

four  days"  tr.mspirati,,,,  at   ,s   ,..    C.      The  nl(>r«   <"    lesstiailsllH  Cllt  lea\  CS 

tissue  w  is  much  collapsed,  the  walls  being  „_  i    ,    __.     .    4i,  ii     i__  ,,  i 

|,l..it.-,i:  .also  shrunken,  but  «  as  before,  and  stems;    the  cells  large  and 

Sified  about  5°  diam-Vfl-  Haber-  thin-walled,  containing  com- 
paratively little  chlorophyll  and  abundantly  supplied  with 
water,  with  few  and  small  intercellular  spaces  and  the  surface 
generally  smooth. 


CHAPTER    XXII. 

HYDROPHYTES. 

444.  IV.  Hydrophytes  may  be  divided  into  three  groups  : 
i.  Slime  plants,  which  grow  in  the  mud  or  slime  at  the  bot- 
tom of  bodies  of  water.      Here  belong  many  algae,  especially 

itoms,  man\-  species  of  low  fungi,  and  bacteria  in  great 
numbers.  2.  Submersed  plants,  either  free  or  attached. 
Many  alga?,  including  both  the  diatoms  and  the  filamentous 
algae,  are  found  floating  in  the  water  at  various  heights, 
sometimes  near  the  surface,  sometimes  more  deeply  submersed. 
Since  their  substance  is  heavier  than  water,  their  capacity  to 
sustain  themselves  depends  upon  the  production  of  gases  in 
the  interior  of  the  cells,  or  upon  the  presence  of  gases  en- 
tangled among  their  filaments.  A  few  of  the  higher  plants 
are  also  found  submerged  and  free,  such  as  the  bladder-worts. 
The  number  of  free-floating  plants  of  the  larger  kinds  is 
small  compared  with  those  attached.  The  higher  algae, 
moss-worts,  fern-worts,  and  seed  plants  are  usually  fastened 
in  the  mud  or  to  sticks  and  stones.  The  thallus  of  the  algae 
is  usually  profoundly  branched  and  the  shoots  of  the  mosses 
are  richly  supplied  with  leaves.  All  of  the  submerged  fern- 
worts  and  seed  plants  are  characterized  by  a  very  thin -walled 
epidermis,  the  absence  of  stomata,  and  the  extensive  surface 
due  to  the  very  profuse  branching  of  the  stems  or  leaves,  or 
to  the  great  number  of  these,  or  to  both.  In  all  cases  the 
extensive  green  surfa<  e  may  be  looked  upon  as  an  adaptation 
to  securing  carbon  dioxide  and  the  manufacture  of  sufficient 

327 


328  PLANT  LIFE. 

food  by  means  of  the  weak  light  in  a  situation  where  there  is 
no  danger  from  lack  of  water.  3.  Floating  or  partly  sub- 
mersedpltuils,  either  free  or  attached.  Many  of  the Tilamerr^- 
tous  algae  ahTT~TiTattmis  float  free  at  the  surface.  The  chief 
characteristics  of  the  higher  floating  plants  which  root  in  the 
mud  are  these  :  their  floating  leaves  are  simple,  little  branched 
or  not  at  all,  roundish  or  elliptical  in  form,  leathery,  and  the 
surface  not  easily  wetted  ;  stomata  are  present  only  on  the 
upper  surface,  and  the  leaf  stalks  are  adapted  in  length 
to  the  depth  of  the  water  in  which  they  grow  ;  the  woody 
tissues  are  either  entirely  absent  or  poorly  developed,  be- 
cause there  is  no  occasion  for  the  transportation  of  water, 
nor  need  of  rigidity,  since  the  medium  in  which  they  grow 
supports  most  of  the  weight. 

445.  Light. — Green  water  plants  are  limited  in  their 
distribution  by  the  depth  to  which  light  can  penetrate  water. 
This  does  not  exceed  even  in  pure  waters  four  or  five  hundred 
meters.  No  seed  plants  have  been  found  at  a  greater  depth 
than  thirty  meters,  and  few  algae  at  a  greater  depth  than 
forty  meters.  Plants  which  are  brought  up  by  dredging 
from  lower  depths  than  this  are  usually  those  which  have 
been  detached  and  sunk. 

446.  The  temperature  of  the  water  is  very  much  less  sub- 
ject to  variation  than  that  of  the  air,  never  falling,  except 
at  the  surface,  below  0.50  C* 

447.  The  movements  of  the  water  are  of  much  importance 
to  plants  in  bringing  air  and  food  materials  to  them.  These 
movements  are  wave  movements,  or  surf,  and  currents. 
Plants  growing  within  the  limits  of  wave  action  are  often 
damaged  or  torn  away  by  the  waves.  The  Sargasso  Sea  is 
marked  by  an  accumulation  of  such  plants,  mainly  of  brown 

*  The  minimum  temperature  of  the  deeper  water  is  usually  stated  as  40 
C,  but  many  observations  upon  Lake  Mendota  by  Birge  have  shown  that 
in  winter  it  falls  nearly  to  zero,  even  at  a  depth  of  eighteen  meters. 


HYDROPHYTES.  329 

algas,  which  have  been  swept  to  the  quieter  parts  of  the  North 
Atlantic  by  currents  after  having  been  detached  by  the  waves. 
Such  plants  may  often  live  for  a  long  time  and  may  even 
continue  their  development. 

Plants  adapt  themselves  to  currents,  such  as  those  in  fresh- 
water streams,  by  their  slender  form,  which  is  characteristic 
of  plants  in  flowing  waters,  as  seen  in  filamentous  alga?  and 
the  much  divided  leaves  of  higher  plants.  Currents  of  water 
act  as  a  stimulus  upon  certain  plants,  producing  a  direct 
reaction  in  the  mode  of  growth. 

448.  The  composition  of  the  water  affects  chiefly  the  dis- 
tribution of  plants,  in  a  manner  similar  to  the  presence  of 
salts  in  the  soil.  In  the  ocean  waters  the  percentage  of  salts 
is  extremely  variable  in  different  regions ;  in  some  places  it 
is  as  low  as  0.5  per  cent. ,  while  in  others  it  reaches  4  per  cent. 
In  fresh  waters  the  differences  in  kind  and  amount  of  dis- 
solved salts  are  chiefly  due  to  differences  in  the  soils  which 
the  streams  drain. 


8  II.  ADAPTATIONS  TO  OTHER  PLANTS. 

449.  Plant  associations. — Each  set  of  external  conditions 
brings  about  the  association  of  certain  plants  with  each  other, 
because  they  have  adapted  themselves  to  those  conditions. 
The  four  groups  just  considered  may  be  looked  upon  as  plant 
societies  of  the  most  general  kind.  Within  each  of  these 
four  it  is  possible  to  distinguish  a  number  of  smaller  societies 
determined  by  a  more  limited  range  of  conditions. 

Besides  these  plant  associations,  however,  there  are  those 
which  are  determined  by  the  relation  of  the  plants  to  each 
other,  as  affording  mechanical  support,  or  assistance  in  the 
work  of  nutrition.  The  plant  associations  of  this  kind  only 
are  now  to  be  considered. 


CHAPTER    XXIII. 

ADAPTATIONS  TO  OTHER  PLANTS  AS  SUPPORTS. 

Certain  plants  serve  others  as  carriers,  acting  purely  as 
mechanical  supports.  To  these  supports  plants  have  adapted 
themselves  in  various  ways.  In  many  instances  dead  objects 
of  similar  form  may  serve  the  same  purpose.  'Hie  supported 
plants  are,  therefore,  partly  independent  of  the  others,  though 
in  most  instances  in  nature  they  rely  upon  living  supports. 

450.  i.  Climbing  plants.  —  Climbing  plants  are  those 
which  develop  lateral  organs,  sensitive  to  contact,  which  be- 
come recurved   or  coil   about  a  support  of  suitable  form  and 

33" 


ADAPTATIONS    TO    OTHER   PLANTS.  331 

si/o,  or  form  adhesive  disks  by  means  of  which  they  cling  to 
rough  surfaces.  These  lateral  organs  are  forms  either  of 
leaves  or  lateral  shoots,  and  are  known  as  tendrils  (figs.  107, 
156).  (For  their  form  see  %  115,  158;  for  their  action, 
II  266,  293.) 

451.  2.  Clambering  plants  are  those  which  form  lateral 
organs  not  sensitive  to  contact,  and  by  means  of  them  sup- 
port themselves  on  adjacent  plants.  Recurved  leaves,  shoots, 
and  prickles  (fig.  115)  may  serve  these  purposes. 

452.  3.  Twining  plants  are  those  which  have  adapted 
their  shoots  to  winding  about  a  support  of  suitable  size.  (See 
If  291.) 

453.  4.  Root  climbers  have  adapted  their  aerial  roots  to 
attaching  the  plant  to  rough  surfaces.  (See  1"  90.)  All  of 
these  organs  are  structures  belonging  to  the  sporophyte,  and, 
therefore,  are  found  only  in  fernworts  and  seed  plants. 

454.  5.  Epiphytes.— Tins  name  is  rather  loosely  applied 
to  those  plants  which  are  attached  to  others  for  mechanical 
support,  and  do  not  derive  food  from  them.  All  kinds  of 
plants  have  representatives  in  this  group.  Algae,  diatoms, 
and  other  small  water  plants  attach  themselves  to  other  alga; 
and  the  higher  water  plants.  Lichens,  liverworts,  mosses, 
ferns,  orchids,  bromelias,  etc.,  are  abundant  upon  trees. 
Epiphytes  are  attached  by  hair-like  rhizoids,  or  by  hold-fasts, 
which  apply  themselves  to  the  roughnesses  or  even  penetrate 
the  outer  dead  parts,  but  do  not  absorb  from  the  living  tis- 
sues of  the  supporting  plant  either  water  or  food  materials. 
The  water  supply  is  provided  for  (1)  by  adaptations  for  ab- 
sorbing rain  or  dew,  mists,  or  even  dampness,  instantly,  either 
by  the  surface,  as  in  algae,  mosses,  and  lichens,  or  by  means  of 
hairs,  as  in  the  Spanish  moss  and  other  seed  plants;  (2)  by 
adaptations  to  catch  the  water  in  living  or  dead  leaves  and 
hold  it,  either  by  capillarity  or  as  a  vessel,  long  after  pre- 
cipitation has  ceased.      Many    of    the   simpler    epiphytes    are 


332  PLANT  LIFE. 

adapted  to  become  dry  without  injury,  while  the  larger  ones 
are  inhabitants  of  moist  tropical  regions,  where  the  danger 
of  drying  is  avoided  and  it  is  possible  to  obtain  an  adequate 
water  supply.  Their  food  materials  are  derived  entirely 
from  the  air  and  the  water  which  falls  upon  them,  while  the 
mineral  salts  are  obtained  from  the  dust  which  has  been 
carried  by  the  air  and  accumulated  upon  the  surface  of  the 
supporting  plant,  or  among  the  mass  of  dead  and  decaying 
leaves  and  other  debris  about  the  base  of  the  epiphyte.  Or- 
ganic matter  from  the  decay  of  the  older  parts  may  also  be 
reabsorbed. 

An  adaptation  to  this  mode  of  life  is  marked  in  the  repro- 
ductive bodies.  Of  all  epiphytes  the  seeds  or  spores  are 
either  light  and  carried  by  the  wind ;  or  the  seeds  are  sticky 
and  carried  by  birds  and  other  animals  ;  or  they  are  eaten  by 
birds  and  voided  upon  the  trees  where  they  are  adapted  to 
germinate. 


CHAPTER  XXIV. 

SYMBIOSIS. 

455.  Living  contact. — Not  only  are  different  species  as- 
sociated through  the  influence  of  similar  surroundings  which 
they  find  congenial,  but  certain  plants  adapt  themselves  to 
such  an  intimate  relation  with  others  that  they  live  in  imme- 
diate contact  with  them.  This  intimate  association  is  known 
as  symbiosis.  When  the  parties  to  symbiosis  stand  to  each 
other  in  the  relation  of  partners,  each  furnishing  certain 
materials  or  conditions  advantageous  to  the  other,  the  asso- 
ciation is  called  mulualistic  symbiosis  or  mutualism.  When  the 
relation  of  the  parties  is  that  of  master  and  slave,  one  indi- 
vidual deriving  advantage  from  the  labor  of  the  other  and  in 
return  furnishing  it  suitable  conditions  for  existence,  the 
association  is  a  form  of  mutualism  known  as  helotism.  Finally, 
when  the  relation  of  the  parties  is  that  of  an  unwilling  host 
and  an  unwelcome  guest,  one  individual  being  fastened  upon 
by  the  other  from  whose  presence  it  is  unable  to  free  itself, 
the  symbiosis  is  called  parasitism.  (See  ^[^[  51,  52,  53, 
222.) 

A.  Mutualism. 

456.  1.  Between  plants  of  the  same  species. — Mutual- 
ism may  occur  between  individuals  of  the  same  species. 
Illustrations  of  this  are  to  be  seen  in  the  massing  of  the 
lower  alg?e  into  colonies,  in  some  of  which  certain  individuals 
may  be  differentiated  from  others  for  the  purpose  of  carrying 
on  a  function  of  advantage  to  the  colony.      (See  12,  13, 

333 


334  PLANT  LIFE. 

20.)     In  a  somewhat  similar  way  certain  bacteria  are  found 
always  massed  into  colonies,  constituting  a  sort  of  thallus  of 


Fig.  371. — A,  serpent-like  colonies  of  Chondromyces  serpens,  composed  of  numerous 
rod-shaped  individuals,  B,  a,  which  multiply  by  fission,  />,  and  secrete  a  mass  of  jelly 
which  holds  them  together.     A  magnified  45  diam.;  B,  750  diam.-  After  Thaxter. 

characteristic  outline  (fig.  371).  In  the  higher  fungi,  also, 
the  mycelium  may  be  looked  upon  as  a  thallus  formed  by  the 
aggregation  of  many  individuals  ;  for,  while  it  is  possible  to 
have  a  mycelium  produced  from  the  development  of  a  single 
spore,  it  is  not  common.  The  mycelium  is  generally  the 
result  of  the  union  of  hyphse  (see  •;  50)  arising  from  many 
spores.  Even  in  such  cases  the  mycelium  may  constitute 
a  single  body,  and  may  give  rise  to  a  single  fructification. 

457.  2.  Between  plants  of  different  species. — Mutual- 
ism is  more  common  between  plants  of  different  species.  It 
takes  the  following  forms: 

458.  (a)  Lodgers. — The  higher  plants  often  shelter 
'various  species  of  lower  ones  within  their  intercellular  cham- 
bers, or  in  pockets  formed  by  lobes  or  bladders  of  various 
sorts.  This  relation  is  especially  common  between  water 
plants  and  algre.  Species  of  Nostoc  live  in  the  intercellular 
spaces  of  liverworts  and  duck-weeds,  in  the  cortex  of  the 
roots  of  some  land  plants,  and  in  the  bladdery  leaf-lobes  of 
liverworts.  Some  species  of  the  higher  alga?,  also,  are 
frequently  associated  with  other  species  to  which  they  attach 
themselves.  That  they  are  not  merely  epiphytic  (see  *"  454) 
is  shown  by  the  fact  that  certain  species  are  found  only  upon 
certain   other  species,  while   they  do  not  grow  upon  other 


.9  YMBIOSIS. 


335 


plants  which  would  furnish  them  similar  external  conditions 
(fig.  372). 


LJ  % 


A  />' 

Fig.  372.  Fig.  373. 

Fig.  372. — A  portion  of  a  filament  of  an  alga  (Ectocarpus^  showing  at  <(  another  alga 
[Entoderma  Wittrockii)  which  has  embedded  itself  in  the  cell-wall.  Magnified  480 
diam. — After  Wille. 
Fig.  373.— A ,  a  tuft  of  rootlets  of  white  poplar  forming  mycorhiza.  Natural  size.  /•'. 
a  portion  of  a  transverse  section  of  one  of  these  rootlets,  showing  the  mantle  of  fungus 
mycelium  and  the  growth  of  the  hyphae  also  in  some  of  the  outer  cells  of  the  root. 
Magnified  ifiu  diam.— After  Kerner. 

459.  (/')  Mycorhiza. — Mutualism  between  the  roots  of  the 
seed  plants  and  certain  fungi  is  common.  Such  a  combina- 
tion of  root  and  fungus  is  called  a  mycorhiza.  The  fungus 
forms  a  jacket  over  the  outside  of  the  root  (figs.  373,  374), 
taking  the  place  and  work  of  the  root  hairs  by  means  of 
strands  of  hyphae  extending  from  the  surface  of  the  fungus 
jacket  (fig.  374)  ;  or  it  grows  inside  the  cells  of  the  cortex 
anil  epidermis,  forming  knotted  masses  (fig.  375);  or  it  is 
•  onfined  to  certain  definite  portions  of  the  roots,  forming 
upon  them  swellings  from  the  si/.e  of  a  hazelnut  to  the  size 
of  a  man's  head.  The  first  form  is  especially  common  upon 
the  roots  of  the  oak,  elm,  walnut,  apple,  pear,  maple,  ash,  and 
related  trees  It  has  also  been  found  11)1011  the  roots  ^\  a 
large  number  of  herbaceous  plants.    The  second  form  belongs 


336 


PLANT  LIFE. 


chiefly   to  the  heaths  and   orchids.     The  third   form   grows 
upon  alders,  bayberry,  etc. 

460.    (c)  Root  tubercles  of  Leguminosse. — A  peculiar  case 

of  mutualism   appears   in   the   bean   family  between  the  roots 

and  bacteria.     The  latter  produce  upon 

the  roots  small  swellings  from  the  size 

of  a  grain  of  wheat  to  that  of  a  hazelnut 

(fig.    376).        The    presence    of  these 


*IG.  375- 
Fig.  374.— Tip  of  a  rootlet  of  beech  {Fagus  sylvatica)  with  fungus  mantle,  the 
hyphae  acting  as  absorbing  organs  in  place  of  root  hairs.  Magnified  too  diam. — After 
Frank. 
FlG.  375.  -  Mycorhiza  of  orchids.  A,  diagram  of  a  longitudinal  section  of  a  root  ;  /,  /, 
the  cells  of  cortex  filled  with  hyphae  of  fungus;  i-,  stele.  Magnified  about  20  diam. 
/>',  a  bit  of  longitudinal  section  of  root  of  Ffeottia,  near  the  tap.  <■,  epidermis  ;  /,  a 
series  of  cortical  cells  filled  with  fungus.  Into  the  ceil  a  (nearer  the  tip  of  root)  the 
hyphae  are  just  entering;  in  the  cells  above  /',  recently  entered,  they  have  only  formed 
a  small  knot  about  the  nucleus.     Magnified  about  200  diam.— After  Frank. 

bacteria,  in  away  yet  unexplained,  certainly  enables  the  plant 
to  use  free  nitrogen  from  the  atmosphere,  while  other  plants 
are  required  to  obtain  it  in  combination  from  the  soil.  The 
enrichment  of  the  soil  by  growing  clover  and  similar  crops 
upon  it  and  plowing  them  under  is  explained  by  their  ability 
thus  to  accumulate  nitrogen  from  the  air. 

461.   3.  Between  plants    and  animals.    -Mutualism    also 


S  YMBIOSIS. 


337 


occurs  between  plants  and  animals.  Various  species  of  plants 
attach  themselves  to  ani- 
mals by  which  they  are 
carried  about.  The  plant 
is  thus  aided  in  obtaining 
the  materials  for  food, 
and  not  infrequently  the 
plant  conceals  the  animal 
from  another  which  seeks 
it  as  prey.  In  this  way 
certain  crabs  are  hidden 
by  algne  attached  to  them. 
One  of  the  most  striking 
cases  of  protective  m  imicry 
is  that  in  which  an  Aus- 
tralian fish  has  acquired 
surface  outgrowths  which 
imitate  almost  precisely  the 
appearance  of  brown  sea- 
weeds, so  that,  when  quiet,  Fig.  376.— a  young  cl 

.        ,       ,         ,.,  cles,   t,   on   the   roc 

it    looks    like   a   stone    to     Uoff. 

which   seaweeds   had   attached    themselves.      Thus    it    often 

escapes  its  enemies,  as  does  the  crab  with  its 

mask  of  real  seaweeds. 

B.     Helotism. 
462.    1.    Fungi    and    algae. — Helotism 
exists  between  fungi  and  algae,  constituting 

FHd?S;  "Ealnil  the  bodies  known  as  lichens,  in  which  the 
'•  fungus  is  the  master  and  the  alga  the  slave. 
(See  ^[  54</,  and  fig.  377.)  The  same 
fungus  may  be  found  enslaving  more  than 
one  species  of  algae  even  within  the  same  mycelium.  The 
prOtonema    of    mosses    or    even    the    leaves    of    some    small 


enveloping  an   alga, 
us.      Mag- 
nified    950     diam. — 
After  Kemer. 


333 


PLANT   LIFE. 


plants  may  be  surrounded  by  a  mycelium.  The  enslaved 
green  plants  are  generally  unicellular  or  filamentous  algae.  It" 
the  latter  are  the  species  whose  colonies  produce  voluminous 
gelatine,  the  texture  of  the  lichen  body  is  gelatinous  ;  other- 
wise it  is  tough  and  leathery.  Some 
of  the  fungi  which  ordinarily  associ- 
ate themselves  with  alga?  to  form 

"^^  f  /^ff?^'--  i    y    'uncns  may  cx'st  *"ree  as  sai)r°- 

phytes.  The  alga  itself  influences 
the  form  of  the  thallus  more  or  less 
profoundly  according  to  its  relative 
amount.  The  same  fungus  associ- 
ated with  different  algre  produces 
lichens  which  are  described  as  dif- 
ferent species,  or  even  as  different 
genera. 

463.  2.  Animals  and  algae. — 
Helotism  exists  between  animals 
and  algae.  Various  simple  animals, 
such  as  radiolaria  stentors,  hydras, 
sponges,  echinoderms,  and  worms, 


^  radiolarian  iLithn- 
cercus  annularis),  one  of  the 
microscopic  single-celled  animals 
with  a  siliceous  skeleton,  .V, 
formed  by  the  outer  portions  of 
the  protoplasm,  E,  which  is  sep- 
arated from  the  internal  proto- 
plasm, J,  by  a  perforated  cap- 
sule, <  ;  mi,  nucleus;  fed, 
threadlike  protrusions  of  the 
protoplasm.     Embedded  in  the 

outer  protoplasm,  E,  are  numer- 
ous "yellow  cells,"  Z,  each  with 
its  own  cell-wall,  nucleus,  and 
chloroplasts.  These  are  an  alga, 

aXLaAZooxanthellanutricola.     enclose   algae    in    their    bodies   and 

Highly      magnified.   —  After 

Butschli. 


manufacture.     The   al 
cellular    forms  which 
division  (fig.  378). 


utilize  the  products  of  their  food 
,ra:  thus  enslaved  are  all  minute  uni- 
multiply  within    the    animal    body  by 


C.     Parasitism. 

464.  1.  Fungi. — A  very  large  number  of  colorless  plants 
have  adapted  themselves  to  live  upon  living  plants  or  ani- 
mals which  they  force  to  act  as  their  unwilling  hosts.  By 
the  presence  of  the  parasite  the  normal  functions  of  the  host 
or  its  normal  growth  or  both  are  more  or  less  seriously  inter- 
fered with,  so  as  to  produce  disease,  slight  or  grave,  local  or 


SYMBIOSIS.  339 

general,  according  to  the  circumstances.      Many  animals  are 


Fig.  379.— Roots  of  a  yellow  Gerardia,  G,  attached  to  the  root  of  a  blueberry  bush,  B. 
They  enlarge  at  the  points  of  contact  and  there  send  haustoria  into  the  host  root. 
Natural  size.— After  Gray. 

thus  preyed   upon   by  bacteria  and  fungi.      Most  communi- 
cable diseases,  such  as   typhoid   fever,  diphtheria,  and  tuber- 


n  dodder  twining  about  a  hop  stem.  All  but  the  uppermost  coils 
show  the  groups  of  wartlike  swellings  trom  whi<  h  haustoria  pi  ni  trate  the  host  stem. 
Natural  51  v        :   I  ■■  rm  nation  ol    ame.    Thi  are  arranged  in  ordi  1 

from  right  to  left,     tn  the  lasl  ound  a  suitable  support  and  has 

absorbed  all  the  reserve  food  in  the  thicl  nd,  which  has  withered  and  died, 

freeing  the  plant  from  the  ground.     Magnified    1  Vfter  Kerner. 


34Q 


PLANT  LIFE. 


culosis,  are  known  to  be  due  to  the  transfer  of  the  parasite 
from  the  diseased  individual  to  the  healthy  one.  In  a  similar 
way  bacteria  live  as  parasites  upon  green  plants,  causing 
disease  and  often  death.  The  number  of  bacterial  diseases 
among  plants  is  relatively  small,  for  comparatively  few  bacteria 
have  been  able  to  adapt  themselves  to  living  in  the  acid  cell- 
sap  of  plants.  The  number  of  diseases  of  plants  due  to 
parasitic  fungi,  on  the  contrary,  is  very  large.  (For  the  mode 
by  which  parasitic  fungi  gain  entrance  to  the  bodies  of  their 
hosts,  see  %  52.) 

465.  2.  Seed  plants. — A  few  seed  plants  have  adapted 
themselves  to  a  parasitic  life  upon  others.  Some  may  be 
reckoned  as  semi-parasitic,  having 
still  green  leaves  and  true  roots. 
In  addition,  however,  special  organs 
are  developed  for  attaching  the 
parasite  to  the  roots  of  other  plants, 
from  which  at  least  a  water  supply 
and  probably  food  materials  are 
absorbed  (fig.  379).  Other  semi- 
parasites,  such  as  the  mistletoe,  at- 
tach themselves  to  the  host  above 
ground,  and  have  no  true  roots  of 
their  own.  Some  parasitic  seed 
plants  twine  about  their  hosts,  into 
which  they  send  absorbing  organs 
by  means  of  which  they  derive  all 
their  food  from  the  host.  Such  is 
the  yellow  parasitic  vine,  known  as 
dodder  (fig.  380,  A).  These  plants 
germinate  in  the  ground,  and  as  seedlings  possess  true  roots, 
but  after  attaching  themselves  to  the  host  the  lower  part 
of  the  stem  dies  away  so  that  the  true  roots  are  transient  (fig. 
380,  B).     Some  root  parasites  begin  to  germinate  upon  the 


Fig.  3S1. — A  twig  infested  with  a 
parasitic  seed  plant  {Apodan- 
thes)  whose  body  is  hidden  un- 
der the  bark  of  the  host,  through 
whi(  h  a  short  branch  bearing  a 
few  scale  leaves  and  a  single 
flower  bursts.  Natural  size. — 
After  Kerner. 


SYMBIOSIS.  34 l 

ground,  but  do  not  pass  beyond  the  first  stages  of  develop- 
ment unless  in  contact  with  the  root  of  the  host  by  which 
they  are  normally  sustained.  Under  these  conditions  they 
then  form  a  conedike  enlargement,  which  unites  with  the 
cortex  of  the  host  root  and  penetrates  to  the  stele.  From 
this  conical  stem  arise  the  aerial  shoots.  Other  parasites 
form  a  network  or  even  a  complete  hollow  cylinder  outside 
the  wood  of  the  host  and  under  the  bark.  From  this 
curious  body  the  few  flowers  break  through  the  bark  and 
appear  upon  the  surface  of  the  root  or  stem  of  the  host,  quite 
as  though  they  were  a  part  of  it  (fig.  381). 


§  III.     ADAPTATIONS   TO  ANIMALS. 

CHAPTER    XXV. 

ANIMALS  AS  FOOD,  FOES,  OR   FRIENDS. 

I.  Carnivorous  plants. 

466.  Nitrogen  supply. — The  ordinary  source  from  which 
green  plants  obtain  nitrogen  for  the  making  of  their  food  is 
the  nitrogen  compounds  dissolved  in  the  soil  water.  Plants 
which  live  where  the  soil  water  contains  little  or  no  nitroge- 
nous material  are  forced  to  resort  to  another  source  of  sup- 
ply. Some  plants  solve  the  problem  by  entrapping  animals, 
deriving  from  their  bodies  the  desired  nitrogen  compounds. 
Such  plants  are  called  carnivorous  plants,  or,  since  the  bulk 
of  their  catch  consists  of  insects,  insectivorous  plants.  The 
catching  of  animals  is  done 

467.  i.  By  pitfalls  and  traps. — (a)  The  various  pitcher 
plants  furnish  a  fine  example  of  well-devised  pitfalls.  The 
leaves  of  these  plants  have  a  deep,  trumpetlike  tube  making 
up  the  body  of  the  leaf;  or  they  carry  at  the  end  of  a  long 
petiole  a  deep  cup  with  a  lid,  as  in  the  tropical  pitcher  plants 
(fig.  382  ;  see  also  fig.  155).  The  tube  is  one-third  or  half 
full  of  water,  in  which  are  always  found  numbers  of  dead  or 
dying  insects.  The  sides  of  the  tube  without  art'  often  made 
attractive  by  gaudy  colors  or  by  lines  of  sweet  secretion, 
which  draw  both  flying  and  crawling  insects.  Within,  its 
surfaces  are  either  excessively  smooth,   so    as    to  afford  no 

342 


ANIMALS   AS   FOOD,   FOES,   OR   FRIENDS.        343 


foothold  to  an  insect  attempting  to  crawl  out ;  or  covered  by 
stiff,  downward-pointing  hairs  to  oppose  its  passage;  or  the 
side  of  the  tube  is  filled 
with  thin  translucent  spots 
through  which  the  cap- 
tives vainly  strive  to  fly, 
while  the  real  opening  is 
concealed.  By  one  or 
other  of  these  means  the 
prey  is  prevented  from 
escaping,  and  sooner  or 
later  is  drowned  in  the 
liquid.  In  this  liquid 
digestive  enzymes  or  bac 
teria  quickly  dissolve  the 
softer  parts  of  the  insect 
bodies,  and  the  soluble 
portions  are  absorbed  by 
the  leaf. 

{b)  The  bladderwort, 
which  abounds  in  quiet 
pools,  furnishes  an  ex- 
cellent illustration  Of  traps  Flr-  382—  A,  trumpet-shaped  sessile  leaf  of  Sar- 
racenia  variolaris,  snowing  thin  membran- 
(fiUS.  78':,  ^84).  UnOll  m,s  windows  in  the  meshes  of  the  veins  of 
\   ©         o    01    o    ~tj  1  the  hood  which  arches  over  the  mouth  of  the 

the    leaves  are    numerous      trumpet.    /;,  cup-shaped  petioied  leal  .if  .\v- 

pentkes  villosa,  with  elevated  lid  and  margin 
minute       bladders,       each       ribbed.    One-third  natural  size.— After Kerner. 

with  a  small   opening   about   which   divergent   hairs  serve  as 

guides  to  the  entrance.     The  entrance  is   lightly  closed  by  a 

flap  of  membrane,  which  is  readily   lifted   by   minute  water 

animals.      After  they  have   passed   through    the   opening    the 

membrane  drops  behind  them,  ami  is  stiff  enough  to  prevent 

their   escape.       Death   ensues  sooner  or   later,  and  absorbing 

hairs    on    the    inner   face  of  the  trap    take  up   the   nutritive 

materials. 


344 


PLANT  LIFE. 


468.   2.   By    adhesive    surfaces. — Animals   are  also  cap- 
tured by  adhesive  surfaces.      These  surfaces  are  covered  by  a 


■S\      I.        ..v         -:■ 


m3^ 


.%i. 


Fig.  383.  — A  bladderwort  {Utricularia  Grafiana),  showing  an  aerial  flower  stalk 
carrying  an  open  flower  and  a  second  one  above  from  which  the  corolla  lias  fallen. 
Some  stems  bear  numerous,  finely  branched  leaves,  /■,  and  others  the  large  bladders, 
/>'.  See  fig.  384.  A  shoot  of  a' smaller  species  is  shown  at  a,  with  bladders  and 
leu  is  on  same  stem.     About  two-thirds  natural  size.— After  Kerner. 


sticky  fluid  secreted  by  numerous  glandular  hairs,  and  upon 
these   many    small    insects    may  be   found   dead.      In   many 


ANIMALS   AS   FOOD,  FOES,   OK   FRIENDS.       345 


cases  the  softer  parts  of  the  insect  bodies  are  digested  and 
absorbed.     It  should  be  noted,  however,  that  adhesive  sur- 


Fig.  384.  B  Fig.  385-  A 

Fig.  384. — A  bladder  of  Utricularia  vulgaris,  halved  lengthwise,  with  an  imprisoned 

crustacean,  Cyclops,     a  to  b,  opening,  with  hairs,  //,  i,  about  it;    b  to  c,  cushion-like 

rim,  b-c  part  cut  through,  d-e  surface  on  which  the  flap,./,  rests,  opening  inwards  only  ; 

g,  wall  of  bladder  set  with  absorbing  hairs  within  and  glandular  hairs  without ;  k,  the 

stalk  (secondary  petiole).     Magnified  20  diam. — After  Cohn. 
Fig.  3S5.— Two  leaves  of  sun-dew  I Drosera  rotundifolia).     A,  in  expanded  position 

showing  the  tentacles.     B,  shortly  after  the  capture  of  an  insect.     The  tentacles  on  the 

right  half  are  indexed  to  bring  the  glandular  tips  in  contact  with  the  prey.     Magnified 

z\  diam. — Alter  Kerner. 

faces  are  also  merely  protective  against  the  visits  of  unwel- 
come guests,  who  steal  nectar  or  pollen.      (See  ^[  488.) 

469.  3.  By  move- 
ments of  traps  and 
adhesive  surfaces. — 
Somewhat  more 
complex  methods  of 
capture  are  exhibited 
by  leaves  which  have 
special  movements 
connected  with  traps 
or  sticky  surfaces. 
The  sundew  of  our 
swamps  has  the  edges 
and  surface   of  the   leaves  covered 


-Sgf? 


Fir..  386.— Cluster  of  leaves  at  the  base  of  flower  stalk 
of  Venus'  fly-trap  {Dioncea    muscf/ula).      One-half 

natural  size.-  Alter  Drude. 


rith  many  outgrowths, 


346 


PLANT  LIFE. 


each  of  which  is  tipped  by  a  large  gland  (fig.  385).  The 
clear,  glistening  fluid,  a  large  drop  of  which  is  secreted 
by  each  gland,  is  sticky  enough 
to  entangle  even  insects  of  con- 
siderable size,  which  alight  upon 
the  leaves.  The  viscid  secretion 
envelops  the  struggling  insect,  and 
at  the  same  time  the  branches  of 
the  leaves  bend  slowly  inward 
until  more  and  more  of  the  sticky 
glands  are  thrust  upon  it.  The 
character  of  the  secretion  then 
changes.  It  becomes 
more  watery  and 
contains  ferments 
which  soon  digest 
the  softer  parts  of  the 


Fig  187. — .-/,  blooming  plant  <>f  Aldrovandia  vesiculosa.  Natural  size.  Vfter 
Drude.  B,  a  single  circle  ol  leaves  seen  from  the  center  above,  slum-inn  stalk  ami 
two  semicircular  lobes.     Magnified]    diam       V.fter  Caspary. 

Fig.  388.  Transverse  section  through  closed  trap  of  A  Idrovandia,  showing  on  inner 
face  long  sensitive  hairs  and  many  absorption  hairs.  Only  the  central  part  is  three 
layers  of  cells  thick;  abroad  margin  is  only  one  cell  thick.  Compare  appearance  in 
''■  fig-  :<s7-     Magnified  2<>  diam. — After  Caspary. 

body.      These  are  absorbed,  and   play  an   important  part   in 
the  nutrition  of  the  plant. 

Dioncea   (fig.  386)   and   its  water   mate,  Aldrovandia   (fig. 
387),  have  leaves  whose  blades  are  somewhat  like  a  spring 


ANIMALS  AS  FOOD,  FOES,  OR   FRIENDS.       347 

trap.  The  blade  is  two-lobed,  with  a  hinge  along  the  middle 
(figs.  205,  388;.  The  hinge  is  in  reality  a  cushion  of  tissue 
upon  the  back,  which  quickly  throws  the  two  halves  of  the 
leaf  together  when  the  sensitive  hairs  on  the  inner  face 
of  the  trap  are  touched.  The  movement  is  sudden  enough 
in  Dioncea  to  catch  the  slow-flying  insect,  or,  in  Aldrovandia, 
the  minute  water  animal.  The  prey  is  prevented  from  escap- 
ing by  the  interlocking,  toothdike  lobes  along  the  edges 
of  the  leaf.  Digestion  and  absorption  of  the  nitrogenous 
materials  follow.* 

II.  Herbivorous  animals. 

470.  Protection. — While  a  really  insignificant  number  of 
minute  animals  are  eaten  by  plants,  a  very  large  number  of 
plants  find  it  necessary  to  protect  themselves  in  some  way 
against  destruction  by  browsing  animals,  insects,  snails, 
and  slugs.  Since  the  animal  world  relies  for  its  food 
supply  ultimately  upon  the  green  plants,  it  is  plain  that 
no  such  protective  measures  are  completely  effective.  The 
protection,  therefore,  may  be  looked  upon  as  a  protection 
against  extermination  rather  than  against  injury.  As  pro- 
tective adaptations  against  browsing  animals  are  usually 
reckoned  : 

471.  1.  Armor,  in  the  form  of  hard,  leathery,  sharp- 
edged,  woollv,  bristly,  or  sticky  parts,  especially  leaves 
(figs.  361,  362,  364,  389);  or  thorns  (figs.  157,  390),  prickles 
(  fig.    115),  or  stinging  hairs  |  fig.  391). 

*Travesties  upon  these  strange  methods  of  nutrition  appear  periodically 
in  newspapers,  and  plants  of  remarkable  size  and  forbidding  aspect  are 
represented  as  capturing  birds,  animals,  and  even  men,  thai  venture  into 
their  neighborhood.  It  should  be  noted,  therefore,  that  in  all  cases  the 
plants  which  capture  animal  food  entrap  only  the  smaller  animal-,  scarcely 
any  of  them,  except  those  caught  by  the  pitcher  plants,  larger  than  the 

common  house  fly. 


348 


PLANT  LIFE. 


472.  2.  Distasteful  or  injurious  substances,  such  as 
volatile  oils,  camphors,  acids,  tannins,  alkaloids,  etc.  The 
milky  juice  of  plants  like  milkweeds,  which         e 

often  contain  acrid  substances,  may  also  be 
protective. 

473.  3.  Mimicry. — Certain  plants  which 
are  not  distasteful  or  disagreeable  have 
adopted  the  same  form  of  leaves  and  stem 
and  the  general  habit  of  those  which  graz- 
ing animals  have  found  distasteful.     This 

mimicry  causes  them  to  be 
avoided,  as  well  as  the  really 
hurtful  ones  which  they  imitate. 


Fig.  389. 


Fig.  390. 


Fig.  389. — Edge  of  a  leaf  of  a  sedge  (Carex  strii  t,i),  showing  alternate  epidermal  cells 
pointed  and  underlaid  by  two  layers  of  mechanical  cells.  Magnified  200  diam.— After 
Kerner. 

Fig.  390. — Part  of  a  shoot  of  barberry  in  spring  showing  leaves  of  preceding  year  as 
persistent  three-pointed  thorns,  in  whose  axils  the  buds  are  developing  into  the  sea- 
son's siioots.     Natural  size. — After  Kerner. 

Fig.  391. — A  stinging  hair  of  the  nettle  {JJrticd)t  in  longitudinal  section,  x,  emerg- 
ence in  which  the  single-celled  hair  abc  is  sunk  below  <il<.  The  knoblike  apex  <  is 
easily  broken  off  because  the  cell  wall  just  below  it  is  thin  and  brittle.  The  oblique 
cutting  edge  left  pierces  the  skin  like  a  hypodermic  needle  and  some  of  the  acrid  cell 
contents  enters  the  wound,  causing  intense  itching.  Magnified  60  diam. — After 
Frank. 

474.   4.   Ants. — In  the  tropics  particularly,  certain  plants 


ANIMALS  AS  FOOD,  FOES,  OR   FN  I  ENDS.       349 


secure  themselves  from  the  attacks  both  of  browsing  ani 
inals  and  leaf-cutting  insects 
by  encouraging  the  presence 
of  colonies  of  warlike  ants 
upon  them  and  making  pro- 
vision for  their  defenders' 
wants.  A  very  large  number 
of  species  *  protect  themselves 
in  this  way.  For  the  ants 
the  plants  provide  (a)  nectar, 


Fig.  392. 


Fig    J93. 


Fig.  392.-P.it  of  a  section  through  the  cushion  («•',  fie;,  303I  at  base  ol  leal  ol  ( 'ecropia, 
showing  the  velvet}  hairs  with  which  it  is  covered,  and  among  them  the  egg-like 
bodies,  rich  in  proteids  and  fats,  whi<  h  the  ants  collect  and  cany  into  their  nests  in  the 
interior  of  the  stem.     Magnified  about  mcliam.     After  Schimper. 

Fig  J93  \pr\  ol  the  hollow  stem  of  a  young  Cecropia.  a,  the  thin  spot  above  a 
leaf,  whii  h  al  lias  bei  11  gnawed  through  by  the  ants  to  make  their  nest  in  the  cavity 
ol  the  stem  :  1  .  the  I  u  hion  at  lias,-  ,.1  I,  .it  si'.ilk  where  food  bodies  grow.  See  fig.  39--. 
Two-thirds  natural  size.     Alter  Schimper. 

similar  to  that  secreted  in  the  flower,  i.e.,  a  watery  solution 
of  various  sugars,  but  secreted  by  nectaries  outside  the 
flower  ;  (//)  fodder,  in  the  form  of  hairs  (fig.  392),  often  of 
peculiar    form,    richly   supplied    with     nutritive    substances, 


More-  than  three  thousand  arc  listed  by  Delpino. 


;;o 


PLANT  LIFE. 


growing  from  special  parts  of  the  surface,  which  are  regularly 
eaten  by  the  ants  and  grow  again,  so  that  a  constant  supply  is 
at  hand;  (c)  divel/ings  of  various  sorts.  Certain  plants  have 
the  stems  hollow  throughout,  with  special  modification  of  the 
structure  at  certain  spots,  so  that  an  entrance  to  these  hollows 
may  be  readily  made  (fig.  393).  In  others,  portions  of  the 
internodes  are  much  enlarged  and  hollow  ;  sometimes  only 
the  internodes  in  the  region  of  the  flower  clusters  are  thus 
transformed.  In  other  plants  chambers  are  produced  by  the 
bladdery  enlargement  of  the  under  part  of  the  leaf  near  the 
midrib  (fig.  394).     In  some  acacias  the  stipules  are  developed 


as  massive  thorns,  which 


the  ants  inhabit. 

475.  Domatia. — Somewhat  sim- 
ilar dwelling  places,  though  less 
perfect,  are  provided  by  many 
plants  for  the  mites.     These  dwell- 


lii 


r 


Fig.  304. 


395- 


Fk;.  394.  — Under  side  of  the  base  of  the  leaf  blade  of  Tococa  lancifolia,  showing 
bladder  on  each  side  of  midrib,  each  with  entrance  at  a,  a.  Natural  size.  (?)— After 
Si  lumunii 

Fig.  395— Domatia  on  under  side  of  leaves.  A,  between  midrib  and  laterals  of 
Psychotria.  8,  between  midrib  and  lateral  of  the  linden  (  Tilia  Europaa).  Magni- 
fied about  5  diam.— After  LundstriSm. 


ing  places  are  in  the  form  of  minute  shelters  usually  upon  the 
under  side  of  the  leaves.  They  are  generally  formed  by  hairs 
roofing  over  an  angle  of  the  veins,  or  by  various  outgrowths, 
folds  and  pits  (fig.  395).  Their  significance  is  not  at  all 
clear. 


ANIMALS  AS  FOOD,  fiOES,   OR   FRIENDS.        35 1 

476.  5.  Crystals.  —  Plants  protect  themselves  against  soft- 
bodied  animals,  such  as  snails  and  slugs,  by  means  of  the 
sharp-pointed  crystals  which  are  present  in  the  leaves  of 
many  species.  According  to  Stahl,  all  tissues  containing 
these  crystals  are  avoided  by  such  animals,  but  will  be  readily 
eaten  by  them  after  the  crystals  are  removed. 


II.  REPRODUCTIVE    ADAPTATIONS. 

CHAPTER    XXVI. 

PROTECTION     AND     DISTRIBUTION     OF     SPORES 
AND    SEEDS. 

The  present  knowledge  of  reproductive  adaptations  among 
the  flowerless  plants  is  very  imperfect,  though  probably  many 
exist.  This  chapter  must,  therefore,  discuss  chiefly  the 
adaptations  in  the  more  complicated  reproductive  structures 
of  seed  plants  which  have  been  most  studied,  with  only 
incidental  allusions  to  such  arrangements  in  the  lower  plants. 

I.  Protection  against  bad  weather. 

477.  By  movements. — Spores  unfitted  to  resist  low  tem- 
peratures or  wetting  must  be  protected  from  rain,  cold,  and 
similar  conditions.  When  nectar  is  secreted  in  the  flower  as 
an  attraction  to  insects  it  is  liable  to  be  washed  out  by  rain 
unless  access  of  water  to  the  interior  of  the  flower  is  pre- 
vented. To  avoid  these  dangers,  many  plants  upon  the 
approach  of  unfavorable  weather  bend  their  leaves  so  as  to 
close  the  flower  (fig.  396),  or  arch  the  stalk  so  as  to  turn  the 
blossom  into  such  a  position  that  the  rain  or  snow  will  not 
reach  the  sporangia  or  the  nectaries.  These  movements  of 
the  leaves  and  stalk  are  combined  in  various  ways  to  meet 
the  needs  of  each  particular  form.      All  of  them  are  growth 

352 


DISTRIBUTION  OF  SPORES   AND    SEEDS.       353 

movements,  brought  about  by  variations  in  light  and  tem- 
perature, which  act  as  stimuli.      (See  ^|  286.) 

II.  Adaptation  to  distribution  of  spores. 
The  fact  that  spores  are  found   in  every  group  of  plants 
from  the  lowest  to  the  highest  makes  it  probable  that  a  great 


Fig.  396.  ''"■  3^7 

Fig.  396.— A,  flower  of  California  poppy  (Eschscholtzia),  opened  in  sunshine  ;   /•'.  the 

same,  closed  in  wet  weather.     Natural  size.  -After  Kerner 
Fig.  V17.     A,  aerial  liypha  of  Pilobolus  crystallinus,  with  sporangium.     The  liypha  is 

swollen  beneath  the  sporangium  and  very  turgid.     />'.  the  same  with  sporangium  torn 

off  at  base  and  being  shot  away  by  the  violent  escape  of  the  mucilaginous  contents  uf 

the  hypha.    Magnified  about  lodiam.    After  Kerner. 

variety  of  ways  will  have  been  adopted  by  plants  to  secure 
their  distribution.  The  more  important  ways  may  be  grouped 
as  follows  : 

478.   1.  By  turgor  and  tension.  —  Among  the  fungi,  spores 
are  often  projected  from  the  spore  case  by  the  pressure  upon 


354 


PLANT  LIFE. 


it    of    neighboring    cells,    increasing    until    the   sporangium 

ruptures  suddenly  ami  the  spores  are  shot  out  like  projectiles. 
In  some  cases  the  whole  sporangium  is  thrown  off  in  this 
fashion,  often  to  the  distance  of  a  meter  or  more  (fig.  397). 


Fig. 


B 

Fig.  398. 

Fig.  398.— A,  a  fly  killed  by  the  fly  fungus  {Empusa  Muscce),  stuck  to  wall  by  hypha 
and  surrounded  by'a  halo  of  the  spores.  Two-thirds  natural  size.  B,  hvph.v  projecting 
into  the  air  from  the  body  of  the  fly,  from  whose  tips  spores  are  being  shot  off. 
Several  are  shown  in  various  stages  of  development.  The  turgor  of  the  enlarged  end 
of  hvpha  finally  ruptures  the  atta<  hment  ol  the  spore  and  it  is  shot  off  surrounded  by 
the  mucilaginous  contents  which  cause  it  to  adhere  to  any  object  struck.  Magnified 
200  diam.  ""  C,  a  spore  enveloped  in  mucilage.     Magnified  420  diam  —  After   Kcrner. 

Fig.  399. —  A,  spore  chain  from  a  fructification  {acidiuni)  of  the  cranberry  rust 
(Calyptrospora).  s,  s,  mature  warty  spores  separated  by  an  intermediate  cell,  w, 
which  has  arisen  by  the  division  of  the  spore  fundament  by  a  transverse  wall  into  a  large 
upper  and  a  small  lower  cell.  The  upper  becomes  the  spore  and  the  lower  thi 
mediate  cell  which  elongates,  loses  its  contents,  and  dies  ;  its  wall  becomes  mucilagi- 
nous and  so  loosens  the  spores.  Magnified  420  diam.— After  Hartig.  B,  three  spores 
at  tip  of  an  acropetal  chain  ;  the  terminal  spore  therefore  smallest  A  disjunctor,  </, 
has  been  formed  between  the  layers  of  the  partition  wall  and  lias  forced  them  apart 
The  white  area  between  two  lowest  shows  area  formerly  connected.  ;/,  nuileus. 
Magnified  520  diam.-  After  Woronin. 

The  fungus  which  attacks  and  kills  house  flies  in  summer 
casts  off  the  single  spore  from  the  end  of  the  stalk  carrying 
it  by  the  bursting  of  the  end  of  this  stalk  through  excessive 
turgor  (fig.  398).      With  the  spore  goes  the  contents  of  the 


DISTRIBUTIOX    OF  STORES   AiYD    SEEDS. 


355 


stalk,  so   that    it   is  surrounded  by  a  mass  of  mucilage,  thus 
enabling  it  to  adhere  to  any  object  which  it  strikes. 

Filaments  carrying  the  spores  often  twist  upon  drying 
and  thus  jerk  off  the  spores  ;is  they  suddenly  slip  past  some 
obstruction.  When  spores  are  produced  in  chains,  either 
the  walls  of  a  special  cell  or  a  layer  of  the  cell-wall  between 
them  may  act  as  a  separator  by  its  alteration  into  mucilage 
(A,  fig.  399).  In  some  cases  the  spores  are  wedged  apart  by 
the  secretion,  between  the  layers  of  the  wall  joining  them,  of 
a  cellulose  plug  which  gradually  elongates  into  a  slender 
spindle  to  whose  tips  the  spores  are  so  slightly  attached  that 
the  lightest  breath  carries  them  away  (B,  fig.  399).  The 
elaters  of  the  liverworts  (fig.  n  and  c  321)  serve  in  some 
cases  to  sling  out  the  spores  when  the  capsule  bursts  ;  in  other 
cases,  as  in  Marchantia,  they  entangle  the  spores,  insuring 
gradual  and  preventing  too  sparing  distribution.  The  teeth 
around  the  mouth  of  the  capsule  of  mosses  serve  to  distribute 
the  spores  at  opportune  intervals,  instead  of  having  them 
emptied  out  all  at  once.  In  some  mosses  the  teeth  are  erect 
or  recurved  when  dry,  but  upon  being  moistened  they  arch 
over  the  mouth,  thus 
forming  a  nearly  closed 
cover  (fig.  400).  <  hints 
have  the  teeth  arched 
over  the  mouth  when 
dry  or  permanently  fas- 
tened together  by  their 
tips,  thus  narrowing  the 
opening  and  allowing 
the  spores  to  sift  out 
between  them.  In  some 
cases  the  teeth,  by  their 
form  and  hygroscopic  curvatures,  serve  to  sling  out  the  spores 
to  a  short   distance.      In  many  ferns   the  annulus  of  the    spo- 


Fig.  4<>"  Capsules  "i  .1  m<.ss  [Grimmia)  afier 
fall  of  lid.  .-J, teeth  erect  when  dry.  leaving  cap- 
Bule  widely  open  ;  /•'.  the  same  in  damp  weather. 
Magnified  about  10  diam.     After  Kerner. 


356 


PLANT  LIFE. 


rangium  tends  to  straighten  itself  upon  drying,  thus  rupturing 
the  sporangium.  After  bending  backward  for  some  distance 
until  the  tear  gapes  wide,  it  suddenly  straightens  and  hurls 
the  spores  to  a  considerable  distance  (fig.  4or). 


Fig.  401.— Sporangia  of  the  male  fern  (Aspidium  Filix-mas)  scattering  the  spores. 
A,  closed;  A',  burst  by  the  drying  of  the  annulus ;  (',  the  annulus  after  becoming 
strongly  recurved  is  just  returning  to  a  nearly  straight  form  and  the  spores  are  thereby 
being  hurled  toward  />'.     Magnitied  about  65  diam. — After  Kerner. 

479.  2.  By  water. — In  perfectly  quiet  water,  distribution 
of  spores  depends  solely  upon  their  own  motor  organs.  Only 
zoospores  (see  ^|  306)  are  so  furnished.  For  these  a  film  of 
water  is  sufficient,  and  they  may  swim  some  distance  over 
what  appear  to  be  merely  moist  surfaces.  Most  of  the  algae 
and  fungi  living  in  water  form  zoospores.  Their  production 
is  often  controlled  by  external  conditions,  the  formation  of 
new  individuals  being  thus  provided  for  when  the  old  are 
threatened  with  destruction. 

In  flowing  water  and  by  currents,  non-motile  spores  are 
readily  distributed.  Even  such  relatively  heavy  spores  as 
the  resting  spores  of  algae  may  be  carried  long  distances  by 
water  currents.  The  microspores  (  pollen)  of  aquatic  seed 
plants  are  sometimes  carried  to  the  stigma  by  water  currents, 
as  in  Vallisneria  |  fig.  402). 

480.  3.  By  air  currents. — Spores  may  be  readily  carried 
by  the  air  on  account  of  their  small  size  and  their  ability  to 


DISTRIBUTION   OF  SPOKES   AND    SEEDS.       357 

withstand  dryness.  Must  spores  float  in  the  air  for  some  time 
like  dust  particles,  and  the  slightest  current  is  adequate  to 
lift  many  and  carry  them  along.      Spores  of  most  non-aquatiG 


Fie.  402.— Pollination  of  eel-grass  (I'allisneyia  spiralis}.  The  large  flower  is  a  pis- 
tillate one.  with  stigmas  .'ringed  on  under  side.  About  it  are  floating  staminate  flow- 
ers in  various  stages  of  development,  having  broken  from  submersed  stems  which 
bore  them.  The  ones  on  the  right  and  left  have  the  boat-shaped  perianth  lobes  turned 
back,  stamens  mature,  and  pollen  exposed  ;  one  has  floated  so  that  the  pollen  is 
brought  into  contact  with  the  stigma  of  the  pistillate  flower.  Magnified  10  diam. — 
After  Kerner. 

fungi,  mosses,  and  fernworts  are  distributed  by  air  currents. 
The  microspores  of  some  seed  plants,  especially  the  common 
forest  trees,  are  carried  in  this  way. 

481.  4.  By  animals,  especially  insects. — It  is  the  seed 
plants,  particularly,  which  have  adapted  themselves  to  the 
distribution  of  spores  by  this  means.  The  development  of 
the  male  plants  in  this  group  must  be  completed  in  tin- 
neighborhood  of  the  female  plants,  tor  the  reason  explained 
in  ^[  386.  The  microspores  must,  therefore,  be  carried  to 
the  ovules  of  gymnospenns  or  to   the  stigmas  of  angiosperms 


358  PLANT   LIFE. 

and  lodged  there.  It  has  been  clearly  shown  not  only  that 
adaptations  for  securing  this  result  have  been  developed,  but 
also  that  there  have  arisen  various  ingenious  adaptations  to 
sec  ure  cross-polli nation  and  to  prevent  close-pollination. 
(See  \  358.)     Some  of  these  may  be  here  enumerated. 

482.  Adaptations  for  cross-pollination.  —  (a)  The  sepa- 
ration of  the  stamens  and  pistils,  staminate  flowers  and  pistil- 
late flowers  being  produced  upon  the  same  plant  or  even  upon 
different  plants  of  the  same  species  ;  (I>)  the  early  ripening  of 
the  stamens  so  that  they  discharge  their  spores  before  the 
stigma  of  the  same  flower  is  exposed  or  receptive,  or  vice 
versa;  (c)  arrangements  preventing  the  pollen  from  reaching 
the  stigma  of  the  same  flower,  vvhi<  h  vary  according  to  the 
different  modes  by  which  the  transfer  of  the  pollen  is  made; 
(J ,  the  failure  of  fertilization  to  occur  when  close-pollination 
happens.  In  such  cases  the  pollen  is  said  to  be  impotent. 
This  means  that  the  male  plants  are  either  not  completely 
formed  by  it,  or  that  their  sperms  do  not  stimulate  the  egg 
to  development. 

483.  Adaptations  for  close-pollination. — But  close-pollin- 
ation, even  though  it  results  in  weaker  offspring,  is  better 
than  entire  failure  to  produce  progeny.  Therefore,  some 
plants  permit  close-pollination  in  the  event  of  failure  to 
secure  cross-pollination,  while  a  few  have  adaptations  which 
insure  it.  Our  common  violets  produce  in  the  late  spring 
and  early  summer  in<  onspicuous  blossoms  which  do  not  open, 
containing  stamens  with  few  pollen  grains.  These  flowers, 
however,  produce  seed  abundantly,  and  always  by  close- 
pollination.  Various  other  species  have  similar  arrange 
ments. 

484.  Adaptations  to  insects.— The  adaptations  to  secure 
cross  pollination  through  the  visits  of  insects  are  so  numerou 
and  so  varied,  and  the  advantage  in  the  number  and  weight 
of  seeds   produced  is  so  marked,  that  for  most  seed  plants 


DISTRIBUTION   OF  SPORES   AND    SEEDS.       359 

cross-pollination  must  be  considered  the  far  more  desirable 
process.  Flowers  are  adapted  to  insect  visitors  in  the  follow- 
ing ways  : 

485.  (</)  Food. — They  provide  for  their  visitors  edible 
substances,  such  as  nectar  and  pollen,*  material  for  nest 
building,  shelters,  or  breeding  places. 

486.  (b)  Advertisements. — They  advertise  the  presence 
of  such  attractions  in  two  ways,  which  are  sometimes  com- 
bined, and  insects  accustomed  to  visit  flowers  quickly  learn 
to  know  what  the  advertisements  mean.  (i)  By  color. 
Flowers  are  so  colored  as  to  attract  notice ;  and  this  is 
further  secured  by  the  large  size  of  individual  flowers  or  by 
massing  many  small  flowers  into  close  clusters.  (ii)  By  odor. 
Odors  are  due  to  volatile  oils,  usually  in  the  epidermis  of  the 
petals  or  sepals,  often  curiously  localized.  Dusk-  and  night- 
blooming  plants  often  have  heavy  odors. 

487.  (c)  Form  and  position  of  parts. — Many  plants  by 
the  form  of  their  flower  leaves  provide  landing  places  for 
welcome  visitors.  Guides  to  the  location  of  the  nectar,  in 
the  form  of  grooves,  folds,  hairs,  lines  of  color,  etc.,  are 
often  present.  The  form  and  position  of  the  stamens  and 
pistils  is  often  such  as  to  insure  the  desired  transfer  of  pollen. 
These  positions  may  be  permanent  or  they  may  be  secured 
by  movements  at  opportune  times.  Among  the  movements 
are  those  due  to  turgor  and  those  due  to  the  presence  of 
motor  organs.  In  a  very  large  number  of  cases,  by  the  form 
of  the  flower-leaves  and  the  essential  organs  the  plant  is 
adapted  to  visitation  by  particular  insects,  and  if  these  are 
not  present,  or  it  their  access  is  denied,  constant  failure  to  set 
seeds  is  the  result.  Thus  one  may  distinguish  plants  adapted 
to  bees,  moths,  butterflies,  flies,  birds,  or  even  snails. 

488.  (d)  Exclusion  of  unwelcome  visitors. — In  addition  to 

*  The  microspores  are  often  produced  in  great  excess  of  the  plant's  own 

needs. 


360 


PLANT   LIFE. 


provision  for  welcome  guests  must  be  enumerated  the  meth- 
ods of  excluding  unwelcome  guests,  which  on  account  of  their 
size  and  habits  are  unable  to  bring  about  the  desired  transfer 
of  the  pollen,  while  at  the  same  time  they  rob  the  plant  of 
nectar    or    pollen    provided    for    more   acceptable    visitors. 


Fk;.  403. — Flower  of  Cobeea  scandens,b&\\eA\  showing  tufts  of  hairs  on  the  base  of 
the  filaments,  of  which  there  are  five  ;  these  close  the  bottom  of  the  corolla  cup  where 
nectar  is  secreted  against  intruders.     Three-fifths  natural  size. — After  Kerner. 


(i)  Various  obstructions  with- 
in the  flower  may  render  ac- 
cess to  the  nectar  impossible 
to  the  smaller  and  weaker  in- 
sects, while  allowing  others 
to  reach  it.  Such  obstruc- 
tions are  formed  by  folds, 
hairs,  and  other  outgrowths 
upon  the  flower  leaves  or  the 
essential  organs  (fig.  403). 
(ii)  Obstructions  outside  the 
/lower  may  exclude  crawling 

Fig.  404.— Flower  of  a  saxifrage .{Saxi/rapa  insects.       Such  are  sticky  Slir- 
controversa),  protected  against    invasion  J 

by  the  numerous  sticky  glandular  hairs  on  faces    an(J     hairs     (fig.     404), 
the  flower  stalk,  ovulary,  and  calyx.    Mag-  v    °       ^    T/» 

nified  several  diam.— After  Kerner.  nioatS  about  the  Stem  formed 

by  cup-shaped   leaves   holding   water,    or    those    formed  by 

water  in  which  swamp  plants  grow.      (iii)  The  time  of  bloom- 


DISTRIBUTION   OF  SPORES  AND    SEEDS.       36 1 

ing  also  prevents  the  visits  of  any  insects  except  those  flying 
at  that  particular  season. 


III.    Adaptations  to  the  distribution  of  seeds. 

489.  After  the  ripening  of  the  seed  various  devices  and 
forces  operate  to  scatter  them  at  as  great  a  distance  as  pos- 
sible from  the  parent,  so  that  the  young  plants  will  not  come 
into  competition  with  the  old  ones  or  with  each  other.  This 
object,  which  is  secured  in  lower  plants  by  the  distribution 
of  the  spores,  can  only  be  attained  in  seed  plants  by  scatter- 
ing the  seed,  because  the  megaspore  is  not  set  free ;   the  ga- 


Fir,.  405.— Elastic  valves  for  slinging  seeds.  A,  fruit  of  wild  geranium  (G.  /,i/«.r/r,-) 
with  1 11  -i-Msii-m  ,  ,il\  \  I  In  live  1  arpels  surround  an  elongated  torus,  from  which  the) 
break  first  at  bottom  ;  curling  upward  suddenly  they  sling  the  seed  out  oi  the  basal 
part  which  has  cracked  along  the  inner  side.  B,  fruit  ol  touch-me-not  \lmpatiens 
noli-me  tangere),  one  sound,  the  other  bursted  'riK-i.nin.-ls  have  curled  up  elasti- 
cally  from  the  base  and  slung  out  the  seeds.    Natural  size.     Aftei  Kemer. 

metophyte  is  consequently  developed  within  the  sporophyte  ; 
and  the  embryo  sporophyte  is  likewise  enclosed   by  the  old 

sporoph]  te      (See  ■   .108.) 


362  PLANT   LIFE. 

The    methods  by   which   distribution    is  secured   may  be 

grouped  as  follows  : 

490.  1 .  Distribution  by  tension  and  turgor. — Some  plants 
(e.g.,  witch  hazel)  as  they  ripen  the  pericarp,  alter  its  tissues 
in  such  a  way  that  the  contained  seeds  are  compressed  when 
the  pericarp  dries,  and  after  it  opens  they  are  pinched  out 
from  the  narrowing  valves,  as  a  wet  apple  or  melon  seed  may 
be  shot  from  between  the  thumb  and  finger.  In  others 
(e.g.,  touch-me-not  and  cranesbill)  the  parts  of  the  peri- 
carp shorten  on  one  side  until  the  strain  breaks  them  loose, 
when  they  become  suddenly  elastically  curled  and  sling 
the  seeds  contained  to  a  considerable  distance  (fig.  405). 
Somewhat  similar  causes,  i.e.,  curvatures  due  to  unequal 
shrinkage  or  swelling  of  the  tissues,  enable  some  fruits 
with  long  awn  or  bristles  to  creep  over  the  ground  or  to 
bury  themselves  in  it  when  al- 
ternately moistened  and  dried 
(fig.  406).  The  pericarp  of  the 
squirting  cucumber  is  so  dis- 
tended by  the  almost  liquid 
pulp  surrounding  the  seeds  that 
it  ejects  the  mass  through  the 
opening  formed  by  its  separa- 
tion from  the  axis. 

491.  2.  Distribution  by 
water. — In  some  plants  this 
is  secured  by  the  fact  that  the 
fruits  open  only  when  moist- 
ened.     In  such  cases  the  seeds  ..  ,     _.  ..,.,. 

lie    406.— Pieces   mli>   which   the  fruit   of 

may  be  either  Washed  OUt  from       storksbill    breaks.     There    are    five    ol 

J  these  each  corresponding  to  .1  carpel  and 

the  opening    pods    by    rain,   or       arranged  on  the   sides   <.i   a   prolonged 

1  °    '  -  torus  as  in  A ,  fig   405.     A,  when  dry  the 

may    be    loosened    in    many     beak  is  spiraHy  .-..iie.!:  a,  when  moist. 

'  -  I  lie  l>asc  is  hard  and  very  slurp.     .Magin- 

other    ways.      The    seeds    are      Bed  about  a  diam.— After  Noll. 

thus  set   free  at  the  time  best  suited  to  their  prompt  germi- 


DISTRIBUTION   OF  SPOKES  AND    SEEDS. 


363 


nation.  Some  plants,  adapted  to  distribution  by  water,  are 
provided  with  floats.  These  floats  may  eonsist  either  of  the 
enlarged  and  bladdery  pericarp  (or  some  portion  of  it),  or 
of  the  spongy,  air-filled  seed  coat.  The  fruits  or  seeds  are 
thus  made  more  buoyant  and  float  upon  the  surface  instead  of 
sinking  as  usual.  Naturally,  water-loving  plants  are  chiefly 
adapted  to  distribution  in  this  manner. 

492.  3.  Distribution  by  winds. — Some  plants  which  secure 
their  distribution  by  winds  are  only  lightly  attached  to  the  soil 
at  maturity,  so  that  they 
are  readily  uprooted  and 
carried  bodily,  when  dry, 
for  considerable  distances 
by  the  wind.  The  transfer 
is  facilitated  by  the  incurv- 
ing of  the  branches  upon 
drying,  so  that  the  uprooted 
plant  is  more  or  less  spheri- 
cal in  outline,  or  by  the  fact 
that  the  plant  is  normally 
spherical  by  the  propor- 
tion of  the  branches.  Such 
plants  are  known  as  "  tum- 
ble weeds.'*  Singly  or  ag- 
gregated in  large  bundles 
they  arc  rolled  over  plains 
and  prairies  for  long  dis- 
tances, shaking  out  their 
seeds  as  they  go,  or  open- 
ing their  fruits  when  moist- 
ened. Another  adaptation 
for  distribution  by  the 
wind  is  the  small  size  of  some  seeds.  Thoseofsome  orchids 
are  so  diminutive  that    it  takes  500,000  to   weigh   1    gram. 


Fig.   107.— Seeds  ol  an  1  ■'■  >  **\ 

with  cells  ol  seed  coal  bladdery  and  filled  with 
air.  These  seeds  are  eje<  ted  From  the  <  apsule 
by  the  contortions  ol  the  hairs  on  its  inner 
faces  which  curve  and  twist  as  the  moisture  in 
the  ah    varii  s.     Magnified    diam      Ifter 


3^4 


PLANT  LIFE. 


Such  minute  seeds  are  readily  blown  long  distances  by 
the  wind.  Relative  lightness  is  also  secured  by  the  con- 
struction of  some  seeds,  which  are  surrounded  by  a  volu- 
minous coat  containing  many  large  air  spaces  (fig.  407). 
Outgrowths  from  parts  of  the  seed  coat  or  pericarp  also  secure 
the  same  end.  In  such  cases  the  fall  of  the  fruit  or  seed 
though  the  air  is  so  retarded  that  it  may  be  carried  laterally 
some  distance  by  the  wind.  No  seeds,  however  small,  float 
long  in  quiet  air,  since  buoyancy  is  derived  only  from  air- 


Fro.  408. — Fruits  with  wings.  A  ,  fruits  of  ailanthus  tree  (A  .  gla  miulosus),  each  carpel 
with  double  wing.  />',  truits  oi  a  maple  tree,  each  carpel  with  a  single  wing.  Natural 
size. — After  Kerner. 


containing  tissues.  A  flattened  form  of  the  fruit  or  seed  is 
very  common,  and  this  form  is  often  exaggerated  by  the 
formation  of  wings,  i.e.,  of  thin  outgrowths  from  the  surface 
(fig.  408).  The  center  of  gravity  in  such  cases  is  so  placed 
that  the  plane  of  flattening  will  be  nearly  horizontal  when  the 
seed  falls.  These  fruits  or  seeds  sink  from  1  to  30  times  as 
slowly  as  the  same  bodies  without  the  wing.  Sometimes  spe- 
cialized persistent  flower  leaves,  either  corolla  or  calyx,  are 
used  for  this  purpose,  as  in  dandelion  and  thistle  (fig.  409). 


DISTRIBUTION   OF  SPORES   AND    SEEDS.       365 

Hairs  of  the  most  various  origin  arc  produced  in  such 
numbers  and  position  as  to  form  either  parachutes  or  tangled 
woolly  envelopes  to  the  fruit  or  sec  Is  (  figs.  410,  41 1). 


Fig.  41" 


Fig.  409.— Heads  of  fruits  of  the  dandelion;  single  fruits  falling,  exposing  common 

torus  and  involucre.     Natural  size.— After  Kernel . 
Fig.  410. — Fruits  of  a  willow,  burst,  and  allowing  the  seeds,  each  with  .1  tuft  of  silky 

hairs  (coma),  to  escape.     Natural  size.  — After  Kerner. 

493.  4.  Distribution  by  animals. — To  secure  this  there 
arc  two  general  methods  observable.  (</)  The  seed  or  fruit 
is  cither  adapted  for  transport  by  adhering  to  the  both- of  the 
animal ;  or  (b)  the  seeds  are  surrounded  by  edible  parts,  and  at 
the  same  time  so  protected  against  the  digestive  juices  that 
they  may  pass  uninjured  through  the  alimentary  canal.  A  few 
plants  are  distributed  by  animals  which  collect  and  hide  their 
fruits  or  seeds  (e.g.,  the  squirrels  1.  The  adhesion  of  fruitsor 
seeds  to  animals,  especially  to  those  which  are  provided  with 


366 


PLANT  LIFE. 


-A  fruit  of  Barbadoes  cotton,  open,  exposing  the  voluminous  hairs  (commer- 
cial cotton)  which  clothe  the  seeds.     Natural  size. — After  Kerner. 


Fig. 


412. 


Fig. 


Fig.  412. — Fruit  of  Agritnonia,  halved;  showing  torus,  carrying  calyx  and  withered 
stamens  above,  covered  with  hooks,  and  enclosing  the  hard  peril  irp,  with  a  single 
seed.  A  pistil  which  did  not  mature  lies  to  the  right.  Compare  torus  in  tig.  288. 
Magnified  about  8  diam. — After  Baillon. 

FlG.  413. — Fruit  of  tick  trefoil  {Desmodium  Canadense).  A,  pods  which  separate  into 
sections,  each  containing  one  seed.  They  are  covered  with  stiff  hooked  hairs,  some 
of  which  are  shown  enlarged  at  />'.  A,  natural  size.  />',  magnified  about  20  diam. — 
After  Kerner. 


DISTRIBUTION   OF  SPORES  AND    SEEDS.      367 


fur,  is  generally  secured  either  by  surfaces  made  adhesive  by 
the  sticky  secretion  from  glandular  hairs,  or  by  the  develop- 
ment of  outgrowths  in  the  form  of  hooks  or  barbed  prickles 
(figs  412,413,  414,415).  A  few  water  animals  and  wading 
birds  distribute  seeds  which . 
happen  to  fall  into  the  mud 
by  the  adhesion  of  this  mud 
to  their  bodies. 

The  fleshy  fruits  with  edible 
parts  are  usually  colored  to 
attract  the  notice  of  the  fruit- 
eating  animals.  Seeds  which 
escape  crushing  by  the  teeth  or 
grinding  in  the  gizzard  are  apt 
to  be  in  condition  to  germi- 
nate when  voided.  The  seeds 
of  the  mistletoe  are  separated 
from  the  pulp  of  the  berry  by 
the   birds    which    eat    them,  Fig.  414.  Fig.  4iS. 

nnrl  eriVtiner  rr>  the*  Kill  or«  FlG'  4J4-— A,  cluster  of  fruits  of  Spanish 
aiHl,  Sticking  tO  tile  Dill,  are  needles  {Bidens  bipinnata).  A.  a  single 
m-i'i„.,1  riff  ,-m  the>  KronoViao  fruit  enlarged,  show in<  barbed  awns,  rep- 
Wipea     OH     Oil     tile     Drancnes      resenting  the  calyx  lobes,  by  which  it  aS- 

nf    trpp«      whprp    thMV    rr*>rmi  heres  -,l'    animals-      A>   natural  size;    A', 

OI     trees,    Wliere    tney    germi-  magnified  2i  diam.— After  Kerner. 

n_j.  FlG.  415.  — Fruit  of  cockle-bur  (  Kanthium 

u<*tCl  strumarium),  halved,  showing  two  seeds, 

'l'h.>  nrl'ii.tQtinn  nf  nlontc  tn  the  u.PPer  "f  which   usually  germinates  a 

1  ne  adaptation  ot  plants  to     NL.ar  iater  ,i,an  tile  lower.    Natural  size 
any  one    of  these   agents    of     AfterArthur- 

distribution  is  likely  to  be  more  or  less  effective  with  other 
agents.  For  example,  the  tufts  of  hairs  which  increase  the 
buoyancy  of  the  seed  in  air  would  be  equally  effective 
should  the  seed  chance  to  alight  upon  water,  or  they  may 
suffice  to  entangle  the  seed  in  the  fur  of  animals. 

494.  Adaptations  for  germination. — Adaptations  for  dis- 
tribution not  infrequently  also  secure  advantage  in  germina- 
tion. It  is  important  for  man)  seeds  that  they  be  anchored 
to  the  ground  when  they  have  once  been  transported,  so  that 


368  PLANT  LIFE. 

they  may  not  be  subject  to  further  disturbance.  Such  an- 
chorage is  sometimes  secured  by  the  transformation  of  the 
outer  layer  of  cells  into  mucilage,  so  that  the  seed,  upon  be- 
coming wet,  is  stuck  fast  to  the  soil  ;  or  by  the  tufts  ot  hair 
which,  once  wetted,  cling  to  the  surface  of  the  earth  ;  or  by 
barbed  bristles  and  hygroscopic  awns  which,  having  become 
entangled  among  the  grass,  work  a  pointed  seed  body  deeper 
by  every  change  of  moisture  (fig.  406). 

Study  of  plants  in  relation  to  their  surroundings,  therefore, 
yields  the  conclusion  that  these  organisms  are  wonderfully 
plastic,  responding  either  temporarily  or  permanently  to 
every  change  in  conditions.  It  is  greatly  to  be  desired  that 
the  too  common  thought  of  plants  as  only  things  to  be  clas- 
sified may  be  replaced  by  the  conception  of  them  as  beings  at 
work,  to  be  studied  alive. 


APPENDIX   I. 
DIRECTIONS  FOR  LABORATORY  STUDY. 

Part   I  :   Morphology. 

I.    ALG^E. 

A.    PLEUROCOCCUS 

i.  Examine  with  a  lens  pieces  of  bark  bearing  Pleurococcus 
and  similar  algae.  Note  the  irregular  distribution  of  the  green 
granular  heaps  of  plants.  Is  there  any  similarity  to  the  distri- 
bution of  higher  plants  over  uncultivated  areas? 

2.  After  soaking  a  piece  of  bark  for  a  few  minutes,  scrape  off 
with  the  nail  or  a  dull  knife  blade  some  of  the  green  material, 
spread  it  as  well  as  possible  in  a  drop  of  water  on  a  slip  of  glass, 
cover  it  with  a  piece  of  thin  glass,  avoiding  air-bubbles,  and 
examine  with  a  lens.  Observe  the  minuteness  of  some  of  the 
specks,  which  are  mostly  single  plants.  The  larger  ones  are 
clusters  of  plants. 

3.  Demonstration.  Examine  slide  under  a  high  power  and 
observe  the  form  and  color  of  single  plants.  Notice  many  con- 
sisting of  two  or  more  cells  still  joined  together,  resulting  from 
cell  division.     (If  19,  fig.  18.) 

B.    NOSTOC  or  RIVULARIA. 

1.  Observe  the  size  and  form  of  the  colonies,  and  the  consist- 
ence of  the  jelly  enclosing  them.     ("    13.) 

2.  Crush  a  bit  of  a  Arostoc  colony  or  a  whole  one  of  Rivularia 
between  two  glass  slips,  remove  the  upper  slip,  cover  with  water 
and  observe  the  coiled  (Nostoc)  or  radiating  straight  filaments 
(Rivularia)  embedded  in  the  jelly.     (Figs.  13,  14.) 

369 


37°  APPENDIX. 


C.   OSCILLARIA. 

1.  Observe  the  color  of  a  bit  of  Oscillaria;  contrast  it  with  that 
of  Pleurococcus.     (•[  n.) 

2.  With  needles  tease  out  the  specimen  in  a  drop  of  water  on  a 
glass  slip;  observe  the  delicate  thread-like  form.     (Fig.  15.) 

3.  Transfer  a  bit  of  living  Oscillaria  to  a  small  glass  dish  or 
white  individual  butter  plate  with  a  little  water;  protect  it  from 
drying  up  with  a  cover;  24  hours  later  observe  the  position  of 
the  filaments.    (•[  14.) 

4.  Demonstration.  Dip  a  considerable  mass  of  Oscillaria  in  hot 
water  for  a  moment  and  put  in  a  white  butter  plate  with  as  small 
a  quantity  of  water  as  will  cover  it.  As  the  water  evaporates 
observe  the  color  deposited  on  the  dish  at  the  edge  of  the  water. 

or  no 

D.   SPIROGYRA. 

If  fresh  material  is  available  examine  a  few  filaments  in  a  white 
dish  for  color.  If  preserved  material  is  used,  stain  red  by 
immersing  for  a  few  minutes  in  eosin  (cheap  red  ink  will  answer). 

Examine  with  a  lens.     Observe: 

1.  Length;  whether  broken  or  whole;  whether  with  or  without 
branches. 

2.  The  delicate  partitions,  like  white  lines,  crossing  the  green 
(or  red)  filaments,  dividing  the  protoplasm  of  one  cell  from 
another.  Can  the  form  of  the  chforoplasts  be  seen?  (Cf.  fig.  24.) 
This  can  be  readily  seen  only  in  the  larger  species.     (T  25.) 

3.  Demonstration.  Mount  a  few  fresh  filaments  in  water. 
Show  under  moderate  power  the  form  of  the  chloroplasts;  the 
reserve  food  nodules;  the  nucleus.     (Fig.  24.) 

4.  Examine  conjugating  specimens  with  a  lens  after  staining. 
Observe  the  conjugating  tubes  connecting  two  filaments  like  rungs 
of  a  ladder  (Tf  361);  the  zygotes  or  zygospores  (^[365)  as  blackish 
dots  in  some  cells.       Are  they  in  one  filament  only  or  in  both  ? 

5.  Demonstration.  Mount  conjugating  filaments  and  show 
the  conjugating  tubes  and  zygospores.     (If  375,  fig.  303.) 

E.  CLADOPHORA. 

If  fresh   material    is   at  hand   observe    in  a  white  dish;  if  pre- 
served specimens  are  used  stain  for  a  few  minutes  in  eosin. 
I.    How  is  the  plant  attached? 


DIRECTIONS    FOR    LIBOR  A  TORY   STUDY.        3/1 

2.  Observe  form  and  particularly  the  abundant  branching. 
Can  a  single  main  axis  be  traced  ?  How  many  branches  arise  at 
one  point  ?     (Fig.  29.) 

3.  Demonstration.  Kill  and  fix  the  protoplasm  of  some  fila- 
ments of  Cladophora  by  placing  them  in  chrom-acetic  acid 
(water,  990  parts;  chromic  acid,  7  parts;  acetic  acid,  3  parts)  for 
1  hour;  wash  out  the  acid  by  placing  them  in  running  water 
for  several  hours  (6-24)  or  in  a  large  dish  of  water  changed 
several  times  in  the  course  of  24  hours;  stain  by  placing  them  in 
alcoholic  borax-carmine  or  hematoxylin  for  several  hours. 
Mount  in  water.  Examine  with  high  power  of  microscope. 
Each  segment  of  the  filament  will  be  seen  to  contain  several 
nuclei  (more  deeply  stained  than  the  body  protoplasm  and  the 
numerous  chloroplasts),  showing  the  segments  to  be  camocytes  and 
not  true  cells.     (1[  28.) 

F.  STONEWORT  (Ckara  sp.). 

Place  the  plant  in  a  glass  dish  with  clean  water.  Set  it  over  a 
black  background  if  preserved  (and  therefore  colorless)  material 
is  used.      If  fresh,  a  white  dish  furnishes  a  good  background. 

1.  From  the  base  of  the  axis  carefully  remove  the  mud  by 
washing.     Observe  the  colorless  rhizoids.     (IT  37-) 

2.  In  the  body  of  the  plant  observe  (a)  the  central  axis;  {/>)  the 
whorls  of  lateral  dwarf  branches  ("leaves")  at  intervals 
("nodes");  (c)  the  single  lateral  axes  arising  among  the 
whorled  dwarf  branches.     (1[  33,  fig.  35.) 

3.  Trace  the  main  axis  to  its  tip.  Compare  the  distance  be- 
tween whorls  toward  the  tip.  How  do  they  stand  close  to  tip? 
Dissect  away  the  outer  ones  successively.      What  is  within  ? 

4.  Demonstration.  Prepare  or  obtain  a  longitudinal  section  of 
the  apex  of  the  axis,  and  show  under  compound  microscope  the 
apical  cell  and  the  differentiation  and  growth  of  its  successive 
segments.     (T[  39,  fig.  38.) 

5.  Compare  the  length  of  the  various  lateral  axes.  Compare 
the  tip  of  any  of  the  long  lateral  axes  with  that  of  the  main  axis. 
What  do  the  observations  show  as  to  the  duration  of  growth  of 
these ? 

6.  Compare  the  length  of  old  and  young  dwarf  branches. 
Compare  their  tips  with  those  of  either  lateral  or  main  axes. 
What  do  these  observations  show  as  to  the  duration  of  growth 
of  the  dwarf  branches?  Observe  the  form  and  distribution  of 
the  branchlets.     Can  they  continue  to  grow  in  length? 


37 '2  APPENDIX. 

7.  Hold  a  bit  of  the  main  axis  (use  decalcified  plants)  between 
the  halves  of  a  piece  of  pith  and  with  a  very  sharp  knife  or  a 
razor  cut  a  transverse  section  of  the  axis.  Mount  on  a  slide  in 
water  with  cover  glass,  and  examine  with  lens.  Observe  the 
central  cell,  surrounded  by  a  row  of  cortical  cells.     (Fig.  37.) 

8.  Trace  the  course  of  the  rows  of  cortical  cells  by  examining 
the  surface  of  the  axis  with  lens.  Note  the  short  projecting  cells 
which  roughen  the  surface.     (If  35.) 

9.  Demonstration.  If  fresh  material  is  available  mount  a  living 
rhizoid  in  water  and  show  the  rotation  of  the  lumpy  protoplasm. 

10.  On  the  lower  whorled  branches  observe  the  black  ovoid 
resting  spores,  surrounded  by  a  paler  cortex,  with  a  crown  of  five 
cells  at  the  free  end.  Study  these  on  successively  higher  and 
higher  branches,  and  observe  differences  in  color,  and  finally  of 
shape.  What  is  the  form  of  the  youngest  (ovary)  ?  (T[  389,  fig. 
3I3-) 

11.  Examine  at  the  same  time  the  spherical  spermaries  (orange 
or  scarlet  in  fresh  specimens)  which  are  found  with  some  ovaries. 
Why  are  they  absent  on  older  branches  ?  Can  any  trace  of  them 
be  found?     (If  383,  fig.  313.) 

12.  Demonstration.  Mount  young  ovaries  and  show  the  central 
cylindric  egg  ;  the  five  cortical  cells,  straight  in  the  youngest, 
spirally  twisted  in  old«r  ones,  terminated  by  five  crown  cells, 
between  which  the  sperms  make  their  way  to  the  egg. 

Mount  entire  spermary;  also  on  another  slide  one  teased  out 
with  needles  ;  show  the  eight  wall  cells,  united  by  zigzag  edges, 
each  carrying  a  handle-cell  on  its  inner  face,  from  which  arise 
numerous  filaments  composed  of  disk-like  cells  each  containing 
one  sperm. 

G.    POLYSIPHONIA  (/'.  variegata). 

Place  a  plant  in  a  glass  dish  over  a  black  or  white  background. 
Observe 

1.  The  form  of  the  body  and  the  mode  of  branching.     (Fig.  39.) 

2.  The  mode  of  attachment  at  the  base,  if  specimens  are  entire. 

3.  Demonstration.  Mount  the  tip  of  one  of  the  branches  and 
show  the  high,  dome-shaped  apical  cell,  with  segments  cut  off 
successively  from  its  base,  to  be  later  themselves  divided 
longitudinally.     (If  39,  fig.  41.) 

4.  Cut  a  transverse  section  of  a  medium  sized  axis  and  observe 
the  four  large  peripheral  cells,  surrounding  a  central  cell;  the 
latter  to  be  seen  only  under  compound  microscope.    (Tf  3S,  fig.  40.) 


DIRECTIONS  FOR    LABORATORY  STUDY.       373 

5.  On  some  plants  observe  that  the  smaller  branches  are 
swollen  here  and  there  with  more  opaque  contents  at  these 
points.  These  are  the  tetrasporangia.  Compare  their  size  as  they 
are  traced  tip-wards.  What  do  you  infer  as  to  their  origin  ? 
(IT  317.  fig-  22Q) 

6.  Demonstration.  Mount  tetrasporic  branches  and  show  the 
tetraspores. 

The  sexual  reproduction  is  so  specialized  that  beginners  should 
not  be  perplexed  with  it.     (See  p.  288.) 

H.    BLADDER  WRACK  {Fucus  vesiculosa). 

Place  plant  in  a  glass  dish  or  a  pan  of  water.     Observe 

1.  The  general  form  of  the  body  or  thallus;  its  mode  of  branch- 
ing.     (IT  41.) 

2.  The  thicker  central  region  forming  a  midrib,  with  thinner 
wings.     (Figs.  42,  43.) 

3.  Downwards,  the  thickening  of  rib  and  death  of  wings  to 
form  stalk  near  base. 

4.  The  lobed  attachment  disk  at  base  of  stalk. 

5.  The  swollen  regions  of  the  wings  here  and  there.  Cut  into 
one  of  these  and  observe  that  it  is  a  bladder. 

6.  The  notched  tips  of  some  branches  ;  the  enlarged  and  more 
or  less  distorted  tips  of  most,  forming  the  receptacles. 

7.  Scattered  on  the  thallus  minute  elevations,  from  which  pro- 
trude through  an  opening  at  the  top  a  tuft  of  fine  hairs.  These 
are  the  mouths  of  the  hair  pits. 

8.  Crowded  on  the  receptacles,  larger  warts  with  a  hole  at  top 
and  similar  protruding  hairs.  These  are  the  mouths  of  larger 
pits,  conceptacles,  which  contain  the  sex-organs. 

Cut  two  thin  transverse  sections  of  the  thallus,  one  through  the 
bladder  and  the  other  through  the  general  thallus.  The  latter 
should  include  a  hair  pit.    Examine  them  with  a  lens  and  observe 

9.  In  the  latter,  the  denser  outer  tissues  ;  the  cortical  region  ; 
the  looser  inner  ones,  of  elongated  threads  and  much  mucilage, 
the  medullary  region  ;  the  thicker  denser  midrib  ;  the  form  of  the 
hair  pit. 

10.  Note  the  difference  between  the  structure  of  the  bladder 
and  the  unswollen  wing.  Which  region  is  altered  to  form  the 
bladder  ? 

Cut  thin  transverse  sections  through  the  center  of  the  recepta- 


374  APPENDIX. 

cles  of  male  and  female  plants.  If  another  species  than  Finns 
vesicuhsus  is  used  (e.g.,  F.  platycarpus)  both  sex-organs  will  be 
found  in  same  conceptacle.  If  the  sexes  were  not  collected 
separately  and  marked  they  can  only  be  recognized  after  cutting 
sections  by  the  descriptions  and  figures  given.     Observe 

ii.  The  form  and  size  of  conceptacles.  Compare  with  hair 
pit. 

12.  In  male  conceptacles,  the  crowded  and  tufted  hairs,  some 
of  whose  terminal  cells  are  spermaries.     (If  381,  figs.  309,  310.) 

13.  In  female  conceptacles,  the  ovaries  of  various  sizes.  The 
larger  ones  are  mature.     (IT  3S9,  figs.  324,  326,  327.) 

14.  Demonstration.  Mount  very  thin  sections  of  male  and 
female  conceptacles  or  some  of  the  teased  out  hairs  from  them 
and  show  : 

The  oval  spermaries,  filled  with  rounded  sperms. 
The  ovaries,  young  and  old  ;  in   the  latter,  the  eight  crowded 
and  therefore  angular  eggs,  which  round  off  on  escape.* 

II.    FUNGI. 

A.    BLACK  MOLD  {Rhizopus  nigricans). 

Before  any  white  or  black  dots  appear  on  the  mold,  examine 
the  vegetative  hyplm.  (""  48.)  These  are  of  two  kinds,  (a)  those 
running  over  the  surface  of  the  bread  ;  (b)  those  penetrating  it. 

1.  Examine  a.  Lift  up  a  few  threads  with  a  needle  and  mount 
them  in  water.  Study  with  a  lens.  Are  they  white  or  colorless? 
Why  then  is  the  body  composed  of  them  (the  mycelium,  ^[  50) 
white  ? 

2.  Examine  /'.  With  needles  tease  out  hyphrc  from  a  bit  of 
bread  in  water  ;  free  them  as  far  as  possible  from  the  debris  and 
mount.      Compare  with  a. 

After  mold  has  begun  to  show  black  dots  (sporangia  )  examine. 

3.  Determine  how  the  branches  are  placed  which  bear  the  spo- 
rangia,    i  Fig.  49.  ) 

4.  Compare  the  white  (young)  and  black  (mature)  sporangia. 
Can  you  find  the  very  smallest  ones? 

*  If  fresh  material  can  be  obtained  demonstrate  the  sperms  and  eggs  after  escape  from 
spermary  and  ovary.  Expose  a  plant  with  mature  receptacles  which  has  been  in  sea 
water  (01  1  ;  pi  1  cent  solution  oi  sea  salt)  to  the  air  for  a  few  hours:  mount  in  sea 
water  on  a  slide  some  of  the  orange  exudation  which  appears  at  the  mouths  of  male  con- 
ceptacles. The  water  will  be  found  filled  with  spei  maries  from  which  are  escaping 
motile  sperms.  The  same  treatment  with  female  plants  will  demonstrate  the  eggs.  By 
mixing  drops  of  water  containing  sperms  and  eggs  the  process  of  fertilization  maybe 
watched. 


DIRECTIONS   FOR   LABORATORY   STUDY.       3/5 

5.  Snip  off  a  few  ripe  sporangia  with  scissors,  handling  them 
cautiously  to  avoid  breaking  or  tangling  them  ;  mount  in  alcohol  * 
and  examine.  Crush  (if  not  already  broken)  and  observe  numer- 
ous dust-like  particles,  the  spores,  which  escape. 

6.  Demonstration.  Mount  a  full  grown  but  immature  sporan- 
gium and  show  the  structure  of  sporangium  with  septum  grown 
up  into  it  forming  the  columella  ;  the  spores.     (1[  316,  fig.  220.) 

B.    WHITE  RUST  (Cystopus  portulaca). 

1.  Demonstration.  Boil  a  leaf  of  purslane  for  a  minute  or  two 
in  s%  potassic  hydrate.  Tease  apart  the  tissues  of  leaf  with 
needles  on  a  slide,  mount  and  show  the  mycelium  of  the  fungus, 
consisting  of  tangled  hyphae  ramifying  among  the  cells  of  leaf. 

(IT  51.  52.) 

Examine  a  dried  leaf.     Observe 

2.  The  white  blisters  {spore  beets)  here  and  there  on  the  surface  ; 
the  thin  membrane  (the  epidermis  of  the  leaf)  by  which  they  are 
covered  ;  in  older  blisters  the  cracking  and  final  disappearance  of 
this  skin.      (IT  312,  fig    210. ) 

3.  The  white  powdery  spores  which  jar  out  or  can  be  dislodged 
with  needle. 

4.  Demonstration.  Cut  a  transverse  section  through  one  of 
these  spore  beds  and  show  the  close  set  ends  of  hyphae  producing 
the  spores  in  chains.      (IT  313. ) 

5.  Cut  a  transverse  section  of  the  leaf  or  stem,  mount  and 
observe  the  numerous  dark  dots  scattered  through  the  tissues  of 
the  host.     These  are  the  resting  spores  with  thick  opaque  walls. 

6.  Demonstration.  Show  in  a  similar  section  the  spermaries 
and  ovaries,  and  the  various  stages  in  the  maturing  of  the  fertil- 
ized egg  into  the  resting  spore. 

C.    MILDEW    {Microsphara   Friesii,  or  Erysiphe  communis). 

Examine  dried  leaf  bearing  mildew.     Observe 

1.  The  whitish  interlacing  hyphne  on  surface  of  leaf,  forming 
the  mycelium.     (If  50.) 

2.  The  distribution  of  the  fungus  ;  does  it  cover  the  whole  leaf 
or  only  occur  in  patches  ?  Compare  the  earlier  and  later  gathered 
leaves  as  to  this. 

•Because  water  will  not  readily  wet  them.  Replace  alcohol  as  it  evaporates  j  it  does 
so  rapidly. 


376  APPENDIX. 

3.  The  pulverulent  appearance  on  the  younger  leaves,  due  to 
spores. 

4.  Demonstration.  Scrape  a  bit  of  the  mycelium  from  the  sur- 
face of  the  leaf  after  moistening  it  for  a  few  minutes  with  a  5$ 
solution  of  potassic  hydrate.  Mount  and  show  (a)  the  colorless 
branching  hyphae  ;  (6)  the  erect  branches  bearing  the  spores  ;  (c) 
the  spores. 

7.  Examine  as  before  one  of  the  older  leaves.  Observe  the 
yellowish  dots  scattered  over  the  mycelium,  the  immature  fruits. 
(U  401,  fig.  337.)  Associated  with  these  the  black  mature  fruits. 
These  contain  sporangia  with  spores.     (*\\  317,  fig.  223.) 

8.  Demonstration.  Mount  and  crush  under  cover  glass  some 
mature  fruits  ;  show  the  sporangia  (asci)  and  their  contained 
spores.     (Fig.  224.) 

D.    CUP-FUNGUS  (Peziza  sp.). 

1.  The  mycelium  penetrates  the  earth  or  rotting  wood  on  which 
the  fructification  appears  and  cannot  be  dissected  out.  Only  the 
reproductive  parts  (T[  317)  are  to  be  examined.  Observe  the  size, 
shape,  and  color  of  the  cup.  The  red  and  orange  cups  usually 
lose  their  color  in  preserved  specimens. 

Cut  a  thin  section  from  a  piece  of  the  cup  at  right  angles  to 
inner  surface.      Mount.     Observe 

2.  The  dense  upper  layer  of  parallel  hyphae  (hytnenium),  with 
rows  of  black  specks.  The  latter  are  the  spores  in  the  long 
parallel  sporangia  (asci).     (H  317,  fig.  222.) 

3.  The  lower  layer,  less  dense,  of  tangled  hyphae. 

4.  Demonstration.  In  a  very  thin  vertical  section  show  (a)  the 
hymenium,  with  paraphyses,  asci,  and  ascospores  ;  (o)  the  looser 
lower  layers  of  interwoven  hyphae. 

E.   LICHEN  (Physcia  stellaris). 

Soften  the  plants  by  soaking  them  in  water  for  a  few  minutes. 
Observe 

1.  The  mycelium,  forming  a  connected  leaf-like  lobed  thallus. 
Compare  as  many  other  forms  as  are  available.     (*}  54a,  fig.  225.) 

2.  Compare  the  color  when  dry  and  wet.  In  the  latter  condi- 
tion, the  mycelium  is  more  translucent  and  the  imprisoned  green 
algae  show  through  more  plainly.     (Figs.  55,  377.) 

3.  The  tufts  of  hyphae  extending  from  lower  surface  to  bark, 
the  holdfasts  or  rliidnes. 


DIRECTIONS  FOR   LABORATORY  STUDY.       377 

4.  Occupying  the  central  region  on  the  upper  surface,  the 
round  colored  disks,  apothecia.  Compare  the  form  of  the  younger 
ones  nearer  the  margin.  What  change  occurs  as  they  grow 
older?     (1  317,  ng-  225-) 

5.  Here  and  there,  minute  black  specks,  the  mouths  of  sacs 
sunk  in  the  thallus,  called  spermogouia. 

Cut  a  vertical  section  through  an  apothecium  and  a  part  of  the 
thallus  on  each  side.     Observe 

6.  The  layers  of  the  thallus;  above  and  below,  dense  layers,  the 
upper  and  lower  cortical  layers  ;  between  them,  the  medullary 
hirer,  with  green  alga  distributed  unequally  through  it. 

7.  The  form  of  the  apothecium  :  its  broad  short  stalk  and 
rim;  the  convex  surface  of  the  disk.  Is  this  more  convex  than 
before  cutting  ?     How  shown  ?     Why? 

8.  The  layers  of  the  apothecium;  the  upper  (liymenium)  of  ver- 
tical parallel  sporangia  containing  rows  of  black  dots,  the  spores ; 
the  second  {sub-hymenium)  of  fine,  pale,  tangled  hyphae;  the  third 
(medullary  layer)  with  green  alga:;  the  lower  cortical  layer.  (Fig. 
226  ) 

9.  Demonstration.  In  a  very  thin  vertical  section  of  apothe- 
cium show  the  sporangia  (asci)  and  ascospores;  the  paraphyses. 

10.  Compare  apothecium  with  the  cup  of  Peziza.  How  are 
they  different?  Do  these  differences  seem  important?  (Figs. 
222,  226.) 

F.   MUSHROOM  (Agaricus  sp.). 

1.  The  mycelium  of  this  plant  consists  of  rope-  or  ribbon-like 
strands  of  hypha  ramifying  extensively  in  the  substratum.  The 
fructification  only  is  here  studied  (Tf  314).  Examine  this  part 
fresh  or  in  water.  Observe  in  a  mature  one  the  two  parts,  stalk 
and  cap.     (Fig.  216.) 

2.  With  a  sharp  long-bladed  knife  or  razor  cut  the  cap  and 
stalk  lengthwise  through  center.  Is  the  stalk  hollow  through- 
out? Or  is  the  central  part  only  of  different  texture  from  outer  ? 
Determine  differences  of  texture  by  teasing  apart  the  hyphse  with 
needles. 

3.  Cut  off  stalk  close  under  the  cap.  Turn  the  latter  under  side 
up.  Observe  the  radial  plates  (gills)  extending  from  margin  to 
stalk.     Do  all  reach  the  stalk  ? 

4.  Examine  the  young  fructifications.  Ry  cutting  them  length- 
wise observe  the  formation  of  the  chamber    from  whose  roof  the 


378  APPENDIX. 

gills  develop;  the  floor  becomes  thinner  as  the  chamber  enlarges, 
and  finally  ruptures,  exposing  the  gills.  Does  any  part  of  this 
floor  (called  the  veil)  adhere  to  the  stalk  or  the  edge  of  cap  on 
mature  fructifications  ? 

5.  If  fresh  mature  fructifications  are  available  cut  away  the 
stalk  and  place  the  cap  on  a  piece  of  black  paper,*  gills  down, 
resting  on  the  stump  of  stalk,  cover  with  a  tumbler  or  bell  jar, 
and  examine  after  24  hours  the  spore  print  formed  by  the  great 
number  of  spores  which  have  fallen  from  the  surface  of  the  gills. 

6.  Demonstration.  Cut  a  very  thin  transverse  section  of  a  gill 
and  show  the  hymenium  covering  the  surface,  with  basidia  carry- 
ing the  free  spores.     (Fig.  213.) 

7.  Compare  with  mushroom  various  other  fructifications  of 
related  fungi  {Hydnum,  Boletus,  Polyporus,  Clavaria).  Observe 
the  various  forms  by  which  extensive  surface  is  secured  for  the 
hymenium.     (T[  314,  figs.  215,  217,  218.) 


III.   BRYOPHYTES. 
A.   THALLOSE   LIVERWORT  {Marchantia  polymorph*). 

Examine  an  entire  plant  in  water.     Observe 

1.  The  flattened  horizontal  body  {thallus)  with  central  line,  the 
midrib,  and  thinner  wings  on  each  side. 

2.  The  notched  apex  (the  apical  cell  is  at  the  base  of  this 
notch).     (%  59.) 

3.  The  mode  of  branching  {dichotomous).  Examine  the  tips 
and  find  one  just  branched.  Do  not  confuse  with  notch  of  apex; 
when  a  tip  branches  there  will  soon  appear  two  notches.  Does 
the  branch  appear  on  the  side  of  the  older  thallus,  or  are  the 
branches  equal  at  first  ?     Are  they  equal  when  older?     (If  58.) 

4.  The  green  lens-shaped  bodies  {brood-buds)  growing  at  certain 
spots  along  the  midrib,  surrounded  by  an  outgrowth  which  forms 
a  cup-like  rim  about  the  cluster.  Remove  a  brood-bud  and  ob- 
serve its  form,  especially  in  full  grown  ones  the  two  opposite 
notches,  the  growing  points.     (1J  362,  fig.  290.) 

5.  The  air  chambers  {areola)  of  the  upper  part  of  the  thallus, 
showing  through  the  skin,  best  seen  in  older  parts  and  with  a 
lens.     What  is  their  form  ?     Are  they  all  alike  ?     (If  57.) 

*  If  the  gills  are  light  colored ;  if  dark  colored  use  white  paper. 


D IKE C I  'IONS  FOK   L A BORA'l 'OK  V   SI' UD  Y.       S79 

6.  The  openings  into  the  air  chambers,  in  the  skin  over  each 
one. 

7.  Compare  the  under  surface  with  the  upper.  Observe  the 
numerous  hairs.  Discover  the  difference  in  place  of  origin  and 
direction  of  growth  of  these.     (^[  56.) 

8.  Carefully  pull  off  with  forceps  as  many  of  these  hairs  as 
possible  and  notice  the  dark-colored  overlapping  outgrowths 
along  the  midrib,  curving  outward  as  they  are  followed  forward, 
attached  along  their  edges.     These  are  the  so  called  "leaves." 

Cut  a  transverse  section  of  the  thallus  through  a  brood-bud 
cup.     Observe 

9.  The  origin  of  the  brood-buds  (only  the  younger  still  remain- 
ing) over  the  midrib. 

10.  The  difference  between  tissue  of  upper  and  under  parts  of 
thallus.  (If  fresh  plants  are  available  observe  especially  the 
difference  in  color.) 

12.  Demonstration.  Cut  a  very  thin  transverse  section  of  the 
thallus.     Select  a  part  passing  through  stoma  and  show 

(1)  The  air-chamber;  its  roof,  the  skin,  with  chimney-like 
stoma  in  center;  its  sides  a  vertical  plate  of  cells;  its  floor,  with 
branched  filaments  of  chlorophyll-bearing  cells.     (Fig.  58.) 

(2)  The  large-celled  colorless  tissue  forming  the  lower  half  of 
section;  the  sections  of  "leaves"  arising  near  midrib  and  con- 
cave towards  center. 

The  sexual  branches  are  so  peculiar  and  specialized  that  the 
beginner  ought  not  to  be  puzzled  with  them. 


B.   LEAFY    LIVERWORT  (Porella  platyphylla). 

1.  In  what  position  do  the  plants  grow  with  reference  to  the 
substratum  ? 

Disentangle  carefully  a  single  plant.*     Observe 

2.  The  growing  apex  ;  the  dying  base;  the  distinctly  dorsiven- 
tral  habit.  Enumerate  the  differences  between  the  upper  and 
under  sides.     (*[  60.) 

3.  The  mode  of  branching  :  a  central  axis,  with  lateral 
branches,  themselves  with  lateral  branches  ;  i.e.,  monopodial  and 
bipinnate.     (If  65.) 

4.  The  yellowish  or  brownish  stem,  covered  with  leaves 
unequally  distributed. 

*  If  dry,  first  soften  by  placing  plants  in  hot  water  for  a  few  minutes. 


3^0  APPENDIX. 

5.  The  two  rows  of  large  leaves  on  the  upper  flanks  of  the 
stem.  How  do  they  overlap?  Turn  the  shoot  over  and  note  a 
third  row  of  small  underleaves  in  the  center  below  ;  also  right 
and  left  the  lobes  of  the  upper  leaves.  Determine  the  form  of 
the  under  and  upper  leaves.  Make  an  enlarged  paper  pattern  of 
the  latter  showing  how  their  ventral  lobes  are  arranged.  (Figs. 
62,  63.) 

6.  Demonstration.  Mount  a  leaf  and  point  out  the  uniformity 
of  cells  and  their  abundant  chloroplasts. 

7.  Examine  male  plants*  and  observe  the  male  branches: 
short,  abundant  near  the  anterior  end  of  main  and  lateral  axes, 
with  crowded,  closely  overlapping  leaves,  the  anterior  ones  often 
pale. 

8.  Cut  off  a  male  branch  ;  dissect  leaves  carefully  and  observe 
in  the  axil  of  each  leaf  a  spherical  yellowish  body  on  a  slender 
stalk,  the  spermary.     (^  3S2,  fig.  311,  B.) 

9.  Demonstration.  Mount  a  mature  but  unbroken  spermary 
and  show  the  single  layer  of  cells  forming  a  wall  enclosing  an 
opaque  mass  of  sperms.  If  fresh,  the  spermary  may  rupture  on 
being  put  into  water  and  the  sperms  swim  about  rapidly  in  the 
field  of  the  microscope. 

10.  Examine  a  female  plant.  On  the  under  side  observe  very 
short  lateral  branches,  bearing  a  pear-shaped  tumid  sac,  the 
perianth.      How  is  it  constructed  at  the  free  end  ? 

11.  Examine  old  perianths;  observe  partly  projecting  from 
such  the  mature  sporophyte,  consisting  of  a  brown  spherical  capsule 
on  a  pale  slender  stalk  (seta).  (The  capsule  is  often  bursted  ;  if 
so,  determine  into  how  many  pieces  (valves)  it  splits.)  To  what 
is  the  stalk  attached  ?     (T[  32,  figs.  64,  65.) 

12.  Examine  successively  younger  female  branches  (to  be 
found  toward  the  anterior  end)  and  note  various  stages  of  devel- 
opment of  the  sporophyte.  Find  a  young  sporophyte,  differenti- 
ated into  stalk  and  capsule,  but  still  enveloped  by  a  thin  mem- 
brane, formed  by  the  enlarged  body  of  ovary  and  surmounted  by 
a  brown  bristle,  the  neck  of  the  ovary.  Determine  what  becomes 
of  this  membrane  {calyptra). 

13.  Demonstration.  Select  the  youngest  female  branch  with 
well  grown  perianth,  cut  a  median  longitudinal  section,  or  dissect 
away  the  perianth,  mount,  and  show  the  group  of  several  ovaries ; 
some  with  canal  cells  in   place,  others  with  canal  cells  disorgan- 

*  The  sexual  organs  are  bome  on  different  plants. 


DIRECTIONS    FOR   LABORATORY  STUDY.       3^1 

ized   making  an  open  canal  to  the  egg,  and  others,  perhaps,  with 
an  embryo  sporophyte  in  the  enlarged  body.     (1[  391,  fig.  331.) 

14.  Demonstration.  From  a  mature  capsule  mount  and  show 
spores  and  elaters.     (Fig.  II,  A.) 

C.  MOSS  [Mnium  cuspidatum). 

Examine  plants  with  capsules  attached.  Observe  the  two 
connected  plants  : 

1.  The  leafy  stemmed  plant  or gametophyte.     (*i\  55.) 

2.  The  slender  plant  attached  to  its  tip,  the  sporophyte,  consist- 
ing of  a  wire-like  stalk,  the  seta,  enlarged  above  to  form  the 
hanging  capsule.      ("IH67,  322.) 

3.  Boil  for  a  few  minutes  in  5  per  cent,  potassic  hydrate,  rinse 
in  water  and  gently  pull  sporophyte  until  it  separates  from  the 
gametophyte.  Observe  the  smooth  pointed  end  which  was  sunk 
in  gametophyte.  If  properly  separated  no  sign  of  tearing  can  be 
seen.     (Fig.  73.) 

Examine  gametophyte  in  water.     Observe 

4.  The  differentiation  of  the  body  into  stem  and  leaves. 

5.  The  brown  hairs  (r/iizou/s)  about  the  stem,  which  attach 
plant  to  ground.     Do  they  branch  ?     (If  62.) 

6.  The  strength  of  the  stem  ;  test  it  by  breaking  it  with  a 
lengthwise  pull.  Cut  a  thin  transverse  section  and  observe  dark 
colored  mechanical  tissues  in  outer  region.      (H  63,  fig.  68.) 

7.  The  form  and  structure  of  the  foliage  leaves  :  note  midrib 
of  mechanical  cells  (test  strength);  lamina  of  one  layer  of  cells 
large  enough  to  be  visible  under  lens  ;  border  of  mechanical  cells, 
some  projecting  pretty  regularly  as  teeth.     (^[64,  fig.  69.) 

8.  Smaller,  scale-like  leaves  on  part  of  the  stem. 
Examine  sporophyte  with  mature  capsule.     Observe 

9.  The  slender  seta. 

10.  The  thin  yellow  inverted  capsule,  from  whose  end  a  piece 
has  fallen  leaving  it  open.     (T  322,  fig.  72.) 

11.  About  the  edge  of  the  capsule  a  fringe  of  pointed  projec- 
tions, teeth,  curved  inward,  constituting  the  peristome.  Break  off 
these  outer  teeth  and  notice  the  pale  fringed  membrane  within, 
forming  the  inner  peristome  or  endostome.     (Figs.  72,  231.) 

12.  Among  these,  or  to  be  pressed  out  of  capsule,  many  fine 
spores. 

13.  Demons/ration.  Cut  off  on  a  slide  the  end  of  the  capsule  as 
a  ring,  with   peristome   attached.      Divide    this    ring   into   halves. 


382  APPENDIX. 

Holding  one  half  with  needle  cut  off  the  peristome  close  to  cap- 
sule. This  allows  the  teeth  to  float  away  from  membrane.  Turn 
other  half  with  convex  side  up,  cover  all  pieces,  and  show  the 
peristome,  endostome,  and  spores. 

Examine  young  sporophytes  of  this  or  other  mosses.     Observe 

14.  The  cylindrical  form  of  the  embryo  sporophyte. 

15.  The  hood  covering  its  apex  and  carried  up  by  it  until  the 
developing  capsule  forces  it  off.     (If  401,  fig.  338.) 

16.  The  lid  which  falls  off  to  open  capsule. 

17.  Examine  on  young  gametophytes  the  sex  organs.  Dissect 
with  needles  the  tufts  of  leaves  at  apex  of  stem*  and  search  for 
(a)  Transparent  oval  sacs,  the  empty  spermaries ;  and  similar 
opaque  greenish  or  whitish  ones,  in  which  sperms  are  still  en- 
closed. (1[  384,  fig.  311,  B).  (b)  Flask-shaped  bodies,  with  a  long 
neck  and  short  stalk,  the  ovaries.  These  may  always  be  found, 
withered  somewhat,  at  the  tip  of  a  stem  where  a  young  sporo- 
phyte is  developing.     (IT  391,  fig.  331.) 

Numerous  hairs,  paraphyses,  of  no  known  function,  may  be 
found  intermixed  with  the  sex  organs. 

19.  Demonstration.  With  dissection  as  above,  mount  spermary 
and  ovary.  Show  (a)  in  spermary,  the  stalk,  the  wall,  the  sperm 
cells  ;  {b)  in  ovary,  the  stalk,  body,  neck,  canal,  and  egg. 

IV.   PTERIDOPHYTES. 
A.    MAIDENHAIR  FERN  {Adiantum pe datum). 

I.  The  gametophyte. 

1.  Observe  its  shape  and  size  ;  the  notch  at  the  growing  point 
(anterior  end)  ;  the  dying  (posterior)  end  ;  the  thicker  central 
region,  with  thin  wings.      [*\]  69.) 

2.  On  the  under  side,  a  cluster  of  rhizoids  near  the  posterior 
end. 

3.  Compare  this  plant  with  the  thallus  of  Marchantia. 

4.  Demonstration.  Mount  a  gametophyte  underside  up,  and 
show  (a)  among  the  rhizoids  the  spherical  spermaries  ;  {/>)  nearer 
the  apex  the  chimney-like  necks  of  the  ovaries. 

If  gametophytes  with  young  sporophytes  attached  are  available, 
observe 

*  In  some  species  the  male  organs  form  at  the  apex  of  the  axis  disk-like  clusters,  sur- 
rounded by  leaves,  the  whole  reminding  one  in  form  of  a  miniature  sunflower-head, 
while  the  female  organs  occur  in  smaller  numbers  (3-6)  in  the  bud-like  clusters  of  leaves 
at  the  apex  of  other  stems. 


DIRECTIONS   FOR   LABORATORY  STUDY.       383 

5.   That  the  young  sporophyte  is  fastened  to  the  under  side  of 
the  gametophyte.     (U  72,  figs.  76-78.) 
II.   The  sporophyte. 
Taking  the  underground  parts  in  a  dish  of  water,  observe 

1.  The  slender  wire-like  roots.  How  are  they  branched  ?  (^[  91 
ff.)  Where  are  they  attached  to  the  stem?  Trace  an  unbroken 
one  to  the  tip.  The  following  points  can  only  be  seen  on  roots 
carefully  gathered  and  cleaned.  What  difference  of  color  near 
tip?  Can  you  find  many  fine  tangled  root  hairs?  Where  present  ? 
Where  absent?     (H  79.) 

2.  Demonstration.  Cut  a  longitudinal  median  section  of  a  root 
tip  and  show  the  tetrahedral  (triangulai  in  section)  apical  cell  ; 
the  segments  cut  off  from  inner  faces  producing  root  tissues, 
those  from  outer  face  producing  the  root-cap.     (U  77,  fig.  S3.) 

Cut  a  transverse  section  of  an  old  root,  mount  and  observe 

3.  The  outer  brown  mechanical  tissues  (also  used  for  storage). 
(H85.) 

4.  The  central  whitish  tissue,  chiefly  the  stele,  in  which  the 
visible  openings  are  the  larger  vessels.     (If  81.) 

5.  In  what  position  does  the  stem  naturally  stand  ?  Observe 
its  occasional  branching  H[  103)  ;  the  surface  covered  with  chaffy 
scales  (![  128)  ;  the  growing  apex  and  dying  base. 

6.  Its  nodes  and  internodes ;  the  nodes  are  indicated  by  the 
attachment  of  a  single  leaf  at  each  ;  the  internodes  are  the  inter- 
vals between  the  nodes.      How  are  the  leaves  placed?     (^[  119.) 

Cut  a  transverse  section  of  the  stem  and  observe 

7.  The   outer   brown   mechanical  tissues  (also  used  for  storage). 

(IT  129.) 

8.  The  circular,  oval,  or  C-shaped  white  tissues,  most  of  which 
belong  to  the  stele.  Trace  the  course  of  the  stele  through  at  least 
two  internodes  by  cutting  a  series  of  rather  thick  (1  mm.)  sec- 
tions, observing  the  mode  in  which  the  stele  branches  to  pass  out 
into  a  leaf.  Cut  also  a  longitudinal  section  through  the  base  of 
a  leaf  stalk  and  trace  course  of  stele.     (H1[  130,  131.) 

Taking  a  perfect  leaf,  dried  under  pressure,  observe 

9.  The  stalk  or  petiole,  with  its  branches.  Note  the  mode  of 
branching;  the  petiole  divides  into  two  equal'divergent  branches  ; 
each  of  these  forks,  one  branch  carrying  leaflets  while  the  other 
again  forks,  and  so  on.     (^[1[  153,  155.) 

10.  The  hardness  of  the  mechanical  tissues  at  surface  of  polished 
petiole. 


3^4  APPENDIX. 

ii.  The  leaflets.  Note  [a)  shape,  as  to  outline  and  margin, 
comparing  basal,  median,  and  terminal  leaflets  of  any  branch  ; 
(b)  the  veins,  containing  branches  of  the  stele  ;  (<r)the  green  tissues 
between  the  veins.     (1[  154.) 

12.  Demonstration.  Strip  off  a  bit  of  epidermis,  mount  and  show 
(a)  the  irregular  form  of  epidermal  cells;  (/<)  the  intercellular 
openings  with  guard  cells  (stomata).     ("  w,   165,  166.) 

13.  Demonstration.  Cut  a  very  thin  vertical  section  of  a  leaf 
at  right  angles  to  veins,  and  show  (a)  the  upper  and  lower  layer 
of  cells  forming  the  epidermis;  (b)  the  green  parenchyma  cells  with 
intercellular  spaces;  (c)  the  section  of  the  vein  composed  of  the 
stele  with  mechanical  tissues  above  and  below  it.     (1T^[  167,  168.) 

14.  At  the  edges  of  the  leaflets  on  the  under  side  crescentic 
brown  spots,  sort.     (Tf  323.) 

15.  Boil  a  leaflet  for  a  minute  in  water.  With  a  needle  turn 
back  a  flap  which  covers  the  sorus,  the  indusium;  observe  that 
it  is  a  specialized  portion  of  the  edge  of  leaflet. 

16.  On  the  under  side  of  the  indusium,  a  mass  of  yellowish 
spheroidal  bodies,  the  sporangia.  Scrape  away  most  of  them  and 
notice  the  relation  of  their  points  of  attachment  to  the  veins. 

Mount  some  of  the  sporangia  and  observe 

17.  Their  shape;  the  stalk  by  which  they  were  attached.  (Fig. 
401.) 

18.  The  darker  ridge,  annulus,  which  serves  to  burst  them 
when  mature.     (Fig.  401.) 

in.  Study  the  manner  of  bursting.  Tear  a  bit  of  indusium  from 
a  dried  specimen  previously  soaked  in  water,  removing  most  of 
the  sporangia.  Allow  it  to  dry  while  watching  it-with  a  lens, 
illuminating  from  above. 

20.  Demonstration.  Mount  sporangia  and  spores  and  show 
their  structure,  especially  the  annulus. 

B.  HORSETAIL  {Equisetum  arvense). 

I.  The  gametophyte  cannot  be  readily  obtained,  and  differs 
from  that  of  the  fern  mainly  in  having  erect  branches,  with  the 
sex  organs  on  the  upper  side  and  always  on  separate  plants.* 

II.  The  sporophyte.  Taking  the  underground  parts  in  water, 
observe 

*  See  Goebel,  Outlines  of  Classification,  figs.  210,  211;  Campbell,  Mosses  and  Ferns, 
fig.  220;  Sachs,  Physiology  of  Plants,  figs.  425,  426. 


DIRECTIONS   FOR   LABORATORY  STUDY.       385 

1.  The  slender  roots  (all  secondary);  their  places  of  origin. 
(1"  7°-)     (Structure  quite  like  ferns.) 

2.  The  stem;  its  nodes  and  internodes;  longitudinal  shallow 
furrows  and  low  ridges. 

3.  At  each  node  a  toothed  sheath  (representing  a  circle  of 
leaves  not  distinct  from  each  other),  best  seen  on  younger  region. 

Cut  a  transverse  section  of  the  stem;  mount;  observe 

4.  A  circle  of  large  air-canals,  one  opposite  each  furrow.  Trace 
these  lengthwise  in  an  internode.  Do  they  pass  the  node? 
(1  129.) 

5.  Within  the  circle  of  air  canals,  the  tissues  constitute  the  stele. 
Opposite  each  surface  ridge,  a  cluster  of  small  cells  looking 
denser  than  adjacent  tissues.  These  are  the  cut  ends  of  the 
vascular  bundles.       (Tf  131.) 

(If  underground  stems  are  lacking  make  out  this  structure  in 
the  aerial  ones,  which  differ  mainly  in  being  hollow.) 

Examine  one  of  the  flesh-colored  aerial  shoots  in  water  (fig. 
235,  A).     Observe 

6.  Similar  distinction  into  nodes  and  internodes.  Break  the 
stem  by  a  lengthwise  pull.  Where  does  it  break?  There  is  an 
intercalary  zone  of  growth  at  the  base  of  internode.  (Compare 
leaves,  ^[  169.) 

7.  The  large  sheath  at  each  node,  the  leaves.  Each  tooth 
represents  a  scale  leaf.  Note  relation  of  teeth  to  ridges  of 
stem  and  to  those  of  sheath  next  above  or  below.     (Tf  160.) 

8.  The  different  leaves  near  apex,  separate,  but  whorled  and 
crowded  in  a  cone;  these  are  the  sporophylls.  (HIT.  324,  325,  fig. 
235.)  Note  the  lowermost  whorl  united  and  forming  a  sort  of 
collar.* 

Dissect  off  several  sporophylls  in  a  small  dish  of  water  and 
observe 

9.  Their  parts,  the  stalk,  the  head ;  hexagonal  form  of  head 
due  to  crowding. 

10.  The  six  to  ten  thin  sacs  under  the  head  and  parallel  with 
stalk,  the  sporangia.     (Fig.  236.) 

11.  Tear  open  a  sporangium.  Leave  the  spores  in  a  pile  on  one 
slide  and  mount  a  bit  of  the  wall  on  another.  In  the  latter  ob- 
serve the  cells  with   thread-like   spiral   thickenings  on  the  walls; 


*  This  may  be  considered  a   primitive  periantli   (.1353)  and  gives  added    reason    tor 
calling  the  whole  cluster  a  Bower. 


386  APPENDIX. 

an   arrangement  to  burst    the    sporangium   when    mature.     (Fig. 
238.) 

Breathe  on  the  dry  mass  of  spores.  Watch  the  squirming 
movements. 

12.  Demonstration.  Mount  a  few  spores  in  water  and  others 
dry,  and  show  the  elaters  ;  strips  of  the  outer  walls  of  spores, 
loosened  but  wrapped  around  spores  when  moist,  straightened 
out  when  dry.     (Fig.  239.) 

Examine  the  green  branched  shoots  (fig.  235,  B).  Compare  struc- 
ture with  other  shoots,  noting  differences.      Observe 

13.  Profuse  branching  and  the  arrangement  of  the  branches  and 
branchlets. 

14.  Cut  a  longitudinal  section  through  the  base  of  a  branch. 
Observe  that  the  branches  arise  from  the  stem  above  the  origin 
of  leaves  and  burst  through  the  sheath. 

15.  That  the  nutritive  work  depends  on  the  stem,  not  on  the 
leaves,  which  lack  green  tissue. 

16.  The  roughness  of  the  surface.  Rub  branches  on  a  metal 
surface  and  observe  that  they  scratch  it,  on  account  of  silica  in 
walls  of  surface  cells. 

C.   SELAGINELLA  (.V.  rupestris). 

I.  Gametophytes,  male  and  female,  are  extremely  reduced, 
scarcely  bursting   the    wall  of  the  spores  producing  them.     See 

IT!  384.  392,  figs.  315,  333. 

II.  Sporophyte. 

Examine  in  water  an  entire  plant.  (If  previously  dry  it  should 
be  boiled  for  a  few  minutes  in  water.)     Observe 

1.  The  yellow  thread-like  secondary  roots  arising  at  various 
points  from  the  stem.     (Structure  like  fern.) 

2.  The  branched  shoots;  note  method  ;  lateral  branches  arising 
from  side  of  mother  shoot,  i.e.,  monopodial  branching. 

3.  The  crowded  foliage  leaves.      Mow  arranged  ?     (See  p.  97.) 

4.  The  sporophylls.  Search  for  ends  of  branches  having  leaves 
in  four  vertical  ranks.  Compare  form  of  these  leaves  with  foliage 
leaves.     Observe 

5.  In  their  axils  large  yellow  sacs,  the  sporangia  ;  some  con- 
taining 

6.  One  to  three  large  spores,  the  megaspores;  more  abundant 
than  similar  sporangia  containing 


DIRECTIONS    FOR    LABORATORY   STUDY.       387 

7.  Numerous  small  spores,  the  microspores.  Microsporangia  are 
usually  at  tip  or  base  of  spike  and  are  often  difficult  to  find  if 
material  is  not  collected  at  proper  season.     (1H[  326,  327.) 

V.   SPERMATOPHYTES.* 

A.   PINE  (Pinus  sylvestris). 

Examine  a  shoot  showing  at  least  the  growth  of  present  year 
and  that  01  the  preceding.     Observe 

1.  Two  kinds  01  axes  :  (a)  the  main  axis  of  the  shoot,  with  un- 
limited growth,  now  terminated  by  a  conical  bud  ;  (/')  the  very 
short  lateral  axes  of  limned  growth,  dwarf  branches,  each  bear- 
ing two  «to/A-/.'i(-r.i.     ("|  no,  rig.  101.) 

2.  The  six  forms  of  leaves.  Scudy  the  shape  and  structure  of 
each.  (a)  the  slender  green  leaves,  needles  ;  (b)  the  scales  closely 
covering  the  older  parts  of  the  stem,  in  whose  axils  arise  the 
dwarf  branches  carrying  the  needle-leaves  ,-  (c)  the  thin  broad 
scales  on  the  dwarf  branches,  enwrapping  the  bases  of  the  needle- 
leaves  (best  seen  about  the  leaves  on  the  young  shoot)  ;  (d)  the 
scales  protecting  the  apical  bud  (If  160)  ;  (<•)  the  two  forms  of 
sporangium-bearing  leaves,  sporophylls,  in  the  two  sorts  of  flowers 
(see  further  4  and  9). 

3.  Dissect  the  scales  carefully  from  a  large  terminal  bud  and 
compare  the  interior  parts  with  those  of  the  shoot  which  bears  it. 
Can  you  make  out  the  corresponding  members?  If  not,  it  is 
because  the  bud  is  too  young.  Use  a  bud  taken  from  the  tree  in 
summer  or  autumn  and  these  points  can  be  seen  best.  What  is  a 
bud?     (p.  85.) 

4.  Examine  the  sporophylls.  Observe  the  two  kinds  :  (a) 
Numerous  oval  clusters  of  yellowish  bodies,  the  micro-sporophylls 
or  stamens,  about  the  base  of  the  young  shoots  (fig.  101),  now 
called  a  staminate  flower  ;  (b)  a  single  cluster  of  mega-sporoph  vlls 
about  the  apex  of  one  or  two  short  lateral  branches  arising  just 
below  terminal  bud  of  a  young  shoot  and  extending  a  little  beyond 
it,  forming  the  pistillate  flower.     (■[*[  331,  344.) 

5.  Study  the  arrangement  of  the  staminate  flowers  on  the  axis. 
Compare  the  position  of  each  cluster  of  sporophylls  (flower}  with 

*  In  this  group  the  sporophytes  only  can  be  studied  without  the  compound  microscope. 
tophytes  sec  demonstration 


388  APPENDIX. 

that   of  the   dwarf  shoots  on   the    upper   part   of  the  same   axis. 
What  is  a  flower?     (p.  236.) 

6.  Dissect  off  a  single  micro-sporophyll  (stamen)  from  one  of 
the  staminate  flowers.  Observe  the  broad  short  stalk  ;  the  thin 
upturned  end  ;  the  two  large  sacs,  sporangia,  on  the  under  side. 
Tear  open  these  and  observe  the  innumerable  small  spores, 
microspores  (or  pollen  grains). 

7.  Demonstration.  Mount  mature  microspores  in  water  and  show 
(<7)  the  spore  itself  (the  central  body)  with  two  bladdery  enlarge- 
ments of  the  outer  wall  to  secure  buoyancy  in  air  ;  [b)  the  immature 
male  gametophyte  inside,  consisting  of  two  cells,  the  smaller  rep- 
resenting the  vegetative  part  (a  mere  rudiment)  and  the  larger  the 
spermary,  simple  by  reduction.      (If  385.) 

8.  Examine  a  pistillate  flower.  Observe  that  it  shows  from  the 
surface  two  kinds  of  leaves:  (a)  thin  ones  with  toothed  edge,  the 
so-called  bracts  ;  (l>)  thick  fleshy  ones  with  a  prominent  point,  the 
carpels.  These  are  probably  two  parts  of  one  structure,  the 
sporophyll,  which  is  deeply  divided  ;  but  there  is  wide  difference  of 
opinion  as  to  the  exact  nature  of  the  bracts  and  carpels. 

9.  Dissect  out  a  carpel  and  observe  (</)  the  broad  attachment  ; 
(/>)  the  ridge  on  the  upper  side  (keel)  extending  into  a  prominent 
point  ;  (c)  the  two  enlargements  on  the  upper  side  near  the  base, 
the  ovules,  and  their  oblique  position.  The  ovules  consist  of  an 
integument  and  a  sporangium  containing  a  single  megaspore. 
Note  the  opening  in  the  integument  (micropyle)  at  the  end  nearest 
the  base  of  the  carpel,  with  two  prolongations  right  and  left. 
(Fig.  246.) 

10.  Examine  a  year-old  cone.  Observe  the  excessive  growth 
of  the  carpels  as  compared  with  the  bracts.  Can  you  find  the 
latter  by  cutting  the  cone  smoothly  lengthwise  through  the  cen- 
ter ?     Note  the  woody  texture  of  all  parts.     (If  404,  fig.  341.) 

11.  Dissect  out  an  entire  carpel.  Observe  the  obliquely  placed 
ovules  (Fig.  342). 

12.  Cut  a  thin  longitudinal  section  of  the  ovules  and  the  carpel. 
Observe  the  sporangium  surrounded  by  the  integument  prolonged 
beyond  it  at  the  orifice  ;  inside  the  sporangium  a  cavity,  the 
interior  of  the  megaspore,  now  partly  filled  with  the  young  female 
gametophyte.     (Compare  fig.  319.) 

13.  Demonstration.  In  a  similar  section  show  these  parts  under 
compound  microscope,  especially  (a)  the  female  gametophyte, 
growing  inside  the  spore  which  has  not  escaped  from  the  sporan- 


DIRECTIONS   FOR    LABORATORY   STUDY.       389 

giuni;  (/•)  microspores  lodged  about  the  mouth  of  integument,  the 
spermary  often  forming  a  tube.     (T|  386.) 

Examine  a  2-year-old  (mature)  cone.     Observe 

14.  The  extreme  woodiness  of  the  cone,  especially  the  carpels 
which  are  spread  apart  when  dry.     y\  404.) 

15.  On  the  upper  surface  of  some  carpels,  two  thin  wing-like 
scales,  with  a  seed  attached. 

16.  Time  the  fall  of  winged  seed  from  the  extreme  height  to 
which  you  can  reach.  Time  its  fall  after  removing  wing.  How 
will  this  aid  in  distributing  seed  ?     (H  492.) 

Bisect  a  seed  lengthwise,  parallel  to  flatter  faces.     Observe 

17.  The  firm  seed-coat,  which  is  the  integument  of  the  ovule 
grown  and  ripened. 

iS.  Enclosed  by  the  coat  a  white  tissue  loaded  with  starch  and 
oil,  the  endosperm,  which  is  the  enlarged  female  gametophyte.  In 
the  center  of  this  the  embryo  sporophyte  which  grew  from  one  of 
the  eggs  produced  by  the  female  gametophyte,  after  the  egg  was 
fertilized.  Note  that  the  tissues  of  the  sporangium  have  disap- 
peared, having  been  crowded  and  absorbed.     (T  403.) 

19.  Dissect  out  the  embryo  from  another  seed.  Observe  that 
it  is  already  differentiated  into  a  slender  stem,  and  six  primary 
leaves  about  its  apex.     (Fig.  339.) 


B.   MARSH  MARIGOLD  (Caltha palustris). 

1.  Examine  the  roots.  Observe  (a)  their  surface,  wrinkled 
from  shortening;  (/')  their  structure. 

2.  Cut  a  transverse  section  as  in  fern;  observe  that  mechanical 
tissues  are  wanting. 

3.  Bisect  longitudinally  the  base  of  a  plant.  Observe,  as  shown 
by  the  origin  of  leaves,  the  variable  length  of  internodes;  at 
base  the  internodes  are  very  short  so  that  leaves  are  crowded; 
in  the  middle  the  internodes  are  long  and  leaves  distant;  above, 
the  internodes  become  shorter  until,  in  the  flower,  they  are  not 
developed  and  the  leaves  are  very  much  crowded.     (^[  119.) 

Study  one  of  the  well  developed  foliage  leaves  (*1  150).  Ob 
serve 

4.  The  broad  rounded  blade  with  slight  branches  (teeth)  at  the 
margin. 

5.  The  long  slender  stalk,  petiole,  gradually  passing  into 


39°  APPENDIX. 

6.  The  sheathing  base,  in  upper  leaves  branched  to  form  two 
stipules. 

7.  Examine  and  compare  the  various  forms  of  leaves:  {a)  the 
lowest,  having  sheathing  bases  without  petiole  or  blade,  passing 
gradually  into  (b)  the  best  developed  foliage  leaves;  (c)  these  near 
the  flowers  losing  petiole  and  diminishing  blade,  becoming  bracts; 
(d)  the  yellow  perianth  leaves  ;  (<r)  next  within  these  the  yel- 
lowish stamens  (micro-sporophylls);  (/)  the  flattened  pod-like 
green  carpels  (mega-sporophylls)  each  forming  a  simple  pistil. 
(11  160,  161.) 

8.  Bisect  a  flower  lengthwise.  Observe  the  three  sorts  of 
leaves,  perianth,  stamens,  and  carpels;  their  relation  to  each 
other  and  their  insertion  separately  on  the  enlarged  stem,  the 
torus.  Separate  some  from  an  old  flower  and  note  the  scars  left 
by  their  fall.     (1  330.) 

9.  Are  perianth  leaves  similar,  or  of  two  sorts?     (1  354.) 

10.  Dissect  off  a  stamen.  Observe  the  two  parts:  (a)  the  slender 
stalk,  filament,  and  (b)  the  enlarged  part,  anther.  Note  in  the 
anther  the  two  lobes,  each  with  a  shallow  groove  marking  the 
position  of  the  two  pairs  of  sporangia.  Tear  open  the  sporangia 
with  a  needle  and  observe  the  innumerable  microspores  (pollen 
grains)  which  they  contain.  Examine  a  naturally  bursted  anther 
and  determine  how  they  open.     (HI  345-348.) 

11.  Demonstration.  Cut  a  thin  section  of  an  anther  from  a  bud 
and  show  (a)  the  four  sporangia,  in  pairs,  entirely  distinct,  and 
the  point  at  which  they  become  confluent  as  they  burst;  (b)  the 
pollen  grains.     (1  351.) 

Dissect  off  and  examine  a  pistil.     (1  33S.)     Observe 

12.  At  the  apex  the  roughened  area,  the  stigma  (1  336),  sessile 
(1  337)  upon 

13.  The  enlarged  part,  the  ovulary  (I335).  Observe  its  flat- 
tened form  and  the  groove  along  one  edge.  Split  it  along  this 
line,  flatten  it  out  carefully  and  note  the  ovules  attached  to  the 
edges.     (1  343.) 

14.  Cut  several  transverse  sections  of  the  pistil  and  observe  the 
thickened  edges  of  the  carpel,  forming  the  placenta,  to  which 
ovules  are  attached.  Compare  sections.  Are  all  ovules  attached 
to  same  edge  ? 

15.  Demonstration.  Prepare  a  longitudinal  section  of  an  ovule 
of  a  lily  and  show  the  two  integuments;  the  sporangium,  enclos- 
ing the  single  megaspore,  or  embryo  sac.      (H  340,  394.) 


DIRECTIONS   FOR    LABORATORY  STUDY.       391 

Study  and  compare  the  flower  and  leaves  of  the  sweet  pea 
(Lat/iyrus  odoratus),  apple,  fuchsia,  and  garden  lily. 

For  the  study  of  primary  roots  and  root  hairs,  primary  stem 
and  primary  leaves,  germinate  Indian  corn,  scarlet  runner  or  any 
bean,  in  clean  damp  pint-  sawdust,  and  grow  until  plants  are  sev- 
eral inches  high,  watching  stages  of  development. 

For  forms  of  stems  examine  white  potato  (tuber);  onion  (bull)); 
Indian  turnip  or  Cyclamen  (corm);  morning  glory  or  hop  (twin- 
ing); white  clover  (creeping). 

For  structure  of  stems,  study  Indian  corn  (monocotyledon,  with 
no  secondary  thickening),  cucumber  or  pumpkin  (dicotyledon, 
with  no  secondary  thickening),  and  young  sunflower  (dicotyledon, 
with  secondary  thickening).      Compare  transverse  sections. 

For  lenticels  and  the  formation  of  periderm,  examine  the  twigs 
of  plum,  cherry,  elder  or  box-elder. 

For  buds  examine  large  winter  buds  of  hickory,  horsechestnut, 
or  poplar. 

Part  II:  Physiology. 

1.  To  show  the  existence  of  turgor  in  the  individual  cell.    (•"  188.) 
Mount  a  bit  of  Spirogyra  under  microscope;  observe  position  of 

chlorophyll  bands.      Irrigate  with  5  per  cent,  solution  of  salt  and 
note  effect. 

(If  Spirogyra  is  not  at  hand  use  hairs  on  stamens  of  Trades- 
cantia  ;  or  the  epidermis,  filled  with  purple  cell  sap,  from  the 
under  side  of  the  leaves  of  the  cultivated  7"radescantia  ("  wander- 
ing Jew");  or  the  hairs  of  geranium  leaves.) 

2.  To  show  effect  of  turgor  of  cells  on  rigidity  of  young  parts  <<>//- 
taining  no  mechanical  tissues,     t".  iSS.) 

Remove  carefully  a  young  plant  with  vigorous  primary  r<>,»t 
grown  in  sawdust  or  sand.  Lay  in  water  for  a  few  minutes. 
Note  rigidity.  Transfer  to  5  per  cent,  salt  solution  for  a  few 
minutes.  Again  note  rigidity.  What  has  happened?  Remove 
to  water  again  for  15  min.      What  is  the  result? 

3.  To  show  the  existence  of  longitudinal  tensions  of  tissues  due  to 
unequal  growth  or  turgor.     ("   259.) 

A.  Cut  a  young  internode  of  elder  10  cm.  long,  making  ends 
as  square  as  possible.  Measure  accurately.  Remove  wood  all 
around   and   measure   pith.      Place    pith    in  an   atmosphere   satu- 


392  APPENDIX. 

rated  with  moisture  and  measure  after  i  hour.  Compare  meas- 
urements. (If  elder  is  not  at  hand  use  young  shoots  of  grape, 
wild  or  cultivated.) 

B.  Split  a  scape  of  dandelion  lengthwise  with  a  sharp  knife 
into  four  strips.  Note  immediate  effect  upon  their  form.  Lay 
the  strips  in  water  for  a  few  minutes.  Observe  form.  Transfer 
them  to  5  per  cent,  salt  solution.  What  effect?  What  causes 
these  changes  of  curvature?  (The  young  stems  (hypocotyls)  of 
castor  bean  may  be  substituted  for  dandelion  scapes  but  are  not 
so  responsive.) 

4.  To  show  the  existence  of  transverse  tensions  of  tissues  due  to 
unequal  growth. 

A.  From  a  piece  of  willow  or  poplar  stem  separate  a  ring  of 
bark  1  cm.  wide,  slitting  it  on  one  side  only,  taking  care  not  to 
stretch  it.  Keep  it  in  a  moist  atmosphere  for  a  few  minutes, 
and  then  replace  it.      Does  it  meet  about  the  wood  ? 

B.  Cut  a  slice  about  2  mm.  thick  from  the  end  of  a  stalk  of 
rhubarb.  Bisect  this  and  keep  the  halves  for  a  few  minutes  in  a 
moist  atmosphere,  then  place  severed  edges  together.  Do  they 
touch  throughout  ? 

5.  To  show  the  location  of  root  hairs  and  especially  their  adhesion 
to  soil  particles.      (H  79,  200.) 

Germinate  wheat  in  sand  and  when  seedlings  have  several 
strong  roots  dig  up  carefully;  shake  sharply  in  water;  note 
where  soil  clings  most  tenaciously.  Brush  away  most  of  this 
with  camelhair  brush  and  examine  a  bit  of  this  part  of  root  under 
a  low  power  of  microscope.  Observe  distortion  of  root  hairs, 
and  particles  of  sand  partly  embedded  in  them. 

6.  To  show  excretion  of  acid  salts  by  roots,     (^f  202.) 

Fill  a  wide-mouthed  bottle  holding  250  cc.  with  tap  water;  add 
2-3  drops  of  ammonia  and  several  drops  of  phenolphtalein.* 
If  the  water  does  not  now  remain  pink  add  a  drop  or  two  more  of 
ammonia.  Select  a  vigorous  seedling  bean  grown  in  sawdust; 
rinse  roots  well  to  remove  impurities. 

Cut  in  two  a  cork  which  fits  the  bottle;  in  the  halves  cut  two 
corresponding  notches  of  such  size  that  with  a  little  cotton  for 
packing    the    plant    will   be    firmly   held.      Place    the    plant    with 

*  An  indicator  for  acids,  colorless  when  a  fluid  in  which  it  is  dissolved  is  acid,  rose 
pink  or  darker  when  alkaline.  For  use  the  crystallized  phenolphtalein  is  dissolved  in 
alcohol. 


DIRECTIONS   FOR    LA  BORA  TORY    STUDY.       393 

enough  cotton  to  secure  it    in  the  cut  cork  and  set  in  bottle  with 
roots  immersed. 

As  the  plant  grows  from  day  to  day  watch  for  the  dis- 
appearance of  color  in  the  solution,  whicn  will  indicate  when  the 
alkaline  fluid  has  become  acid.  Arrange  a  control  experiment  in 
exactly  the  same  way,  but  without  plant.  Surround  each  bottle 
with  opaque  shade  of  heavy  paper,  to  avoid  effect  of  light  on  the 
roots  and  fluid. 

7.  To  show  the  corrosion  of  carbonate  of  lime  by  the  carbonic  acid 
excreted  by  the  roots.     (T  202.) 

Cover  a  polished  marble  slab  to  a  depth  of  5  cm.  with  clean 
sand,  in  which  plant  corn  or  beans.  After  the  plants  are  10-15 
cm.  high,  remove  sand  carefully  and  rinse  off  the  marble. 
Examine  the  surface  by  reflected  light.  A  little  graphite  rubbed 
into  lines  etched  by  roots  will  make  them  more  readily  visible. 

8.  To  show  root  pressure  as  a  factor  in  the  movement  of  water  in 
plants.     (Tf  205,  fig.  172.) 

Cut  off  the  stem  of  an  actively  growing  plant  (plants  of  castor 
bean  and  tomato  25-30  cm.  high  are  especially  recommended) 
a  short  distance  above  the  soil  and  fasten  tightly  to  the  stump, 
by  means  of  rubber  tubing,  a  piece  of  glass  tubing  a  meter  long, 
and  about  the  diameter  of  the  stump.  Add  enough  water  to  rise 
10  cm.  above  the  rubber  connection.  Keep  roots  well  watered  and 
mark  the  height  of  the  water  in  tube  from  time  to  time  until  it 
reaches  the  top  or  begins  to  fall.   Does  the  water  rise  from  the  first  ? 

A  more  satisfactory  record  may  be  reached  by  attaching  to  the 
stump  a  T-tUDe  as  shown  in  fig.  172.  To  the  horizontal  arm 
attach  a  mercury  manometer.  (A  manometer  may  be  readily 
constructed  by  bending  a  glass  tube,  about  5  mm.  diameter  (3 
mm.  bore)  and  80  cm.  long,  upon  itself  30  cm.  from  one  end,  so 
that  it  forms  a  u  with  unequal  legs  3-4  cm.  apart.  Bend  5  cm. 
of  the  end  of  the  short  leg  at  right  angles,  in  the  plane  of  the  U- 
Tie  the  legs  to  a  piece  of  cork  between  the  legs  near  top,  so  that 
the  tube  will  not  be  easily  broken  by  the  leverage  of  the  legs  <'ii 
the  bottom  bend.)  Fill  the  space  between  stump  and  mercury 
with  water.  In  the  third  arm  insert  a  short  tube  drawn  out  to  .1 
slender  point  to  permit  the  escape  of  air  and  extra  water.  Seal 
this  with  flame  after  filling.  There  must  be  at  least  15  cm.  of 
mercury  in  (J  portion  of  manometer.  At  beginning  mark,  with  a 
bit  of  gummed  paper,  height  of  mercury  in  each  leg  ;  measure 
difference  at  intervals  thereafter  until  mercury  begins  to  fall. 


394  APPENDIX. 

9.  To  show  that  water  is  not  absorbed  by  leaves  in  quantity  ade- 
quate to  supply  evaporation.     (^[  196.) 

Cut  off  a  vigorous  shoot  of  a  plant  with  abundant  foliage  ; 
close  end  of  stem  with  grafting  wax  ;  expose  to  sunlight  until 
slightly  wilted  ;  then  immerse  it  in  water.  Does  the  plant  recover 
its  turgidity  ? 

10.  To  show  that  many  leaves  are  not  wetted  by  -water.     (*[  210.) 
Immerse  various  sorts  of  leaves  in  water.      Does  the  water  wet 

the  surface?  What  is  the  cause  of  the  silvery  reflection  of  light 
from  the  surfaces  of  some  ?  What  relation  does  this  repulsion  of 
water  have  to  blocking  of  stomata  by  rain? 

11.  To  show  the  loss  of  -water  by  evaporation.     (If  208.) 

Clean  and  dry  the  surface  of  a  pot  in  which  a  thrifty  single- 
stemmed  plant  is  growing  ;  close  the  hole  in  the  bottom  with  a 
cork  ;  with  a  brush  paint  the  whole  surface  with  a  thick  layer  of 
melted  paraffin.  Cut  out'a  piece  of  stiff  paper  which  will  fit 
around  stem  and  just  cover  the  soil  in  pot.  Using  this  as  a  pat- 
tern cut  a  cover  for  the  soil  from  a  sheet  of  lead  ;  slit  the  cover 
from  the  central  hole  to  circumference  ;  adjust  it  around  plant 
and  cement  all  cracks  with  grafting  wax.*  Weigh.  Weigh  again 
at  intervals  of  24  hours,  for  4  days. 

12.  To  show  the  variation  in  the  rate  of  evaporation  due  to  the 
difference  in  structure  of  the  organ.     (^\^\  209,  438.) 

Compare  as  shown  by  shrinkage  or  by  loss  of  weight,  (a) 
Through  cork  tissue  and  without  it.  Take  two  potatoes  ;  peel 
one  ;  expose  side  by  side  ;  compare  day  by  day.  (b)  Through  skin. 
Compare  in  same  way  two  apples,  (c)  Through  stomata.  Take 
three  equal  leaves  of  oleander;  of  one  close  the  stomata  (which 
are  on  under  side  only)  with  a  thin  coat  of  grafting  wax,  or  cocoa- 
butter  melted  and  brushed  on  (taking  care  not  to  kill  cells  by 
having  wax  too  hot)  ;  coat  the  upper  surface  of  second  in  same 
way  ;  leave  third  uncovered.     Compare  day  by  day. 

13.  To  show  the  conditions  affecting  evaporation.      (^T  210.) 
Construct  a  potometer  as  follows  :    Bend  the  central  stem  of  a 

T-tube  until  it  is  parallel  with  the  cross  piece.  Fit  into  the  lower 
opening  of  the  straight  leg  a  capillary  tube  30-40  cm.  long,  with 
3  cm.  of  each  end  bent  at  right  angles  to  the  main  part  and  in 
opposite  directions.  Into  the  bent  leg  fit  a  shoot  of  a  thrifty 
plant  cut  off  under  water,  at  the  same  time  filling  the  j-t"be  with 

*Or  the  pot  can  be  set  in  a  tin  vessel  which  it  fits  and  the  lead  cover  luted  to  this. 


DIRECTIONS  FOR   LABORATORY  STUDY.       395 

water.  (To  accomplish  this  bend  the  shoot  to  be  cut  of?  so  that 
the  place  of  the  cut  is  submerged  in  a  deep  pan  of  water.  Fit  it 
in  tube  without  exposing  cut  surface  at  all  to  air.)  Dip  the  lower 
end  of  the  capillary  tube  in  water  and  allow  apparatus  to  stand 
until  capillary  tube  fills  with  water.  Remove  the  water  for  a 
moment  and  allow  a  bubble  r  cm.  long  to  enter  ;  time  it  as  it 
moves  between  a  series  of  equidistant  marks  on  capillary  tube. 
Try  the  rate  under  various  conditions  of  light,  temperature,  and 
moisture  acting  on  shoot. 

14.  To  show  the  lifting  power  of  evaporation.     (^[  207.) 

Cut  off  under  water  a  shoot  from  a  thrifty  plant  ;  fasten  it  air- 
tight in  the  end  of  a  piece  of  glass  tubing  30  cm.  long,  of  appro- 
priate diameter,  by  means  of  a  piece  of  rubber  tubing  slipped 
over  the  end  of  the  stem,  taking  care  not  to  expose  the  cut  end  to 
air.  Fill  glass  tube  with  water  before  fitting  in  plant  ;  erect  the 
whole  with  lower  end  of  tube  dipping  in  a  cup  of  mercury.  Set 
in  light  and  note  height  of  mercury  in  1-48  hours. 

15.  To  show  loss  of  liquid  water  when  absorption  is  great  and 
evaporation  slow. 

Grow  seedlings  of  wheat  or  oats  until  5-10  cm.  high  ;  then 
cover  with  a  glass  bell  for  an  hour  or  two.  Where  do  drops  of 
water  appear  ?     Why? 

16.  To  show  roughly  the  path  of  evaporation  stream  in  woody 
plants.      (U  206.) 

A.  From  a  leafy  shoot  of  a  woody  plant  remove  a  ring  of  bark 
5  mm.  wide.  Protect  the  exposed  surface  against  drying  with 
grafting  wax.  Observe  whether  the  leaves  wilt  or  not,  and  if 
they  wilt,  the  time  required. 

B.  With  a  knife  or  fine  saw  cut  a  little  over  half  through  the 
stem  of  a  plant  of  the  same  sort  used  in  A  ;  1  cm.  above  this  cut 
make  a  similar  one  on  the  opposite  side.  The  two  must  be  so 
placed  and  of  such  a  depth  that  all  the  tissues  are  severed.  Sup- 
port the  branch  or  stiffen  it  against  breaking  by  bandaging  it  with 
strips  of  wood.  Make  same  observations  as  in  ./.  Examine  the 
pith.  Is  it  alive  ?  Dues  it  contain  water  ?  1  n  what  tissues,  there- 
fore, do  you  infer  water  travels  to  leaves? 

17.  To  show  restoration  and  maintenance  of  an  interrupted  evap- 
oration stream. 

Fit  a  well  wilted  shoot  into  the  short  arm  of  an  unequal  U-tubc 
filled  with  water  to  the  level  of  the  short  end.  Allow  it  to  stand 
for  half  an  hour.     Does  the  shoot  recover?     If  not,  pour  nun  ut  \ 


39^  APPENDIX. 

into  the  longer  arm  until  it  stands  10  cm.  above  its  level  in  the 
short  arm.  Does  the  shoot  now  recover  turgor  ?  Why?  Allow 
it  to  stand  for  some  days.    Does  the  level  of  the  mercury  change  ? 

18.  To  show  in  what  tissues  food  most  readily  travels.     (U  235.) 
Girdle  as  in  experiment    16  A  a  shoot  of  willow.     Cut  it  off  5 

cm.  below  ring.  Place  shoot  in  water.  After  some  weeks  note 
where  new  roots  are  formed.     Why? 

19.  To  show  the  permeability  of  stomata  for  air  and  their  com- 
munication -with  the  system  of  intercellular  spaces.     (^T*[  167,  227.) 

Fasten  a  leaf  with  a  long  petiole  air-tight  in  a  rubber  cork, 
through  which  also  passes  a  short  glass  tube.  Fit  the  cork  into 
a  bottle  holding  sufficient  water  to  cover  end  of  petiole.  Attach 
a  filter  pump  or  air  pump  to  glass  tube.  Observe  whether  air 
bubbles  leave  the  end  of  the  leaf  stalk. 

Reverse  the  leaf,  so  that  the  blade  is  immersed,  and  make  same 
observation.  Where  do  bubbles  appear  ?  Is  there  any  difference 
between  upper  and  lower  sides? 

20.  To  show  the  depth  to  which  light  may  penetrate  green  tissues. 

a  231.) 

Take  a  cylindrical  pasteboard  or  metal  tube,  closed  at  one  end 
and  having  a  cover  which  will  fit  over  the  closed  end.  In  the 
end  and  in  the  cover  cut  corresponding  holes  1  cm.  in  diam.  Mark 
side  and  cover  when  in  place  so  that  holes  can  be  made  to  coin- 
cide. On  the  bottom  place  a  part  of  a  leaf  which  will  cover  hole. 
Slip  on  cover  and  observe  whether  light  is  transmitted  through 
leaf.  Add  successive  pieces  of  leaf  until  no  more  light  passes. 
What  is  the  color  of  last  light  seen  ?  The  examination  must  be 
made  with  direct  sunlight,  and  light  completely  excluded  from  the 
eye  except  that  which  passes  through  the  instrument. 

21.  Method  for  detecting  considerable  quantities  of  starch  in  plant 
organs.     (1  233.) 

Boil  a  few  leaves  of  various  plants  for  a  few  minutes.  Place 
in  alcohol  at  about  6o°  C.  until  all  chlorophyll  is  dissolved.* 
Bring  the  leaves  into  a  tincture  of  iodine,  diluted  to  a  bright 
brown,  for  half  an  hour.  The  leaves  or  parts  containing  starch 
will  become  bluish,  dark  blue,  or  black,  according  to  amount  of 
starch  present. 

22.  To  show  that  manufacture  of  starch  occurs  only  in  cells  directly 
illuminated.      ("[  231.) 

*  Do  not  heat  over  open  flame,  but  set  bottle,  loosely  corked,  in  a  vessel  of  hot  water. 


DIRECTIONS   FOR   LABORATORY  STUDY.       397 

Darken  portions  of  some  leaves  of  a  plant  previously  found  to 
show  starch  in  its  leaves  (sunflower,  bean,  tomato,  or  nasturtium) 
by  attaching  two  plates  of  cork  on  opposite  sides  by  means  of 
two  pins  driven  through  both  and  the  leaf.  On  the  afternoon  of 
the  following  day,  if  sunny,  cut  off  the  leaves  and  test  for  starch. 
What  has  become  of  starch  in  cells  under  the  cork? 

23.  To  shozu  that  oxygen  is  a  by-product  of  photosyntax,     ("]f  250.) 
Collect   the  gas   mixture   evolved   from  a  vessel  full  of  aquatic 

plants  by  inverting  over  them  a  funnel  to  whose  tip  is  connected 
a  test  tube  filled  with  water  to  be  displaced  by  the  rising  gases. 
Keep  the  plants  in  sunlight.  When  the  tube  is  filled,  test  the 
contents  for  oxygen  by  inserting  a  glowing  splinter. 

24.  To  show  the  effect  of  light  and  temperature  on  photosyntax, 
using  the  rate  of  evolution  of  oxygen  as  an  index. 

Fasten  a  shoot  of  a  water  plant  (Elodea ,  Myriopkyllum,  or  Cerat- 
ophyllum)  10  cm.  long  to  a  glass  rod  and  immerse  in  tap  water  so 
that  the  cuf  end  is  uppermost.  Set  in  sunlight  and  observe  the 
bubbles  rising  from  the  end  of  stem.*  Determine  rate  at  which 
they  rise  by  counting  the  number  given  off  in  a  certain  short 
time.  Continue  the  observation  until  the  rate  is  approximately 
uniform.  Shade  the  shoot  and  determine  rate.  Return  to  sun- 
light and  determine  rate.  Put  a  piece  of  ice  in  the  water  and  de- 
termine again. 

25.  To  show  the  digestion  of  starch  by  diastase.     (*[  237.) 
Powder  a  handful  of   malt  in  a  mortar  or  obtain  ground  malt. 

To  25  grams  of  the  powder  add  100  cc.  of  water;  stir  well  to- 
gether; allow  mixture  to  stand  (with  occasional  stirring)  one  to 
two  hours;  filter;  preserve  the  filtrate.  Take  1  gm.  of  starch 
and  rub  it  up  in  a  dish  with  5  cc.  water;  pour  this  into  gjjj^c.  of 
boiling  water,  stirring  as  it  enters.  With  25  cc.  of  this  paste  mix 
thoroughly  5  cc.  of  the  filtrate  (which  contains  diastase  extracted 
from  the  malt).  Test  a  small  portion  of  the  mixture  at  once  for 
starch  by  adding  a  few  drops  of  tincture  of  iodine,  and  similar 
portions  at  intervals  of  half  an  hour  until  starch  reaction  ceases. 
Taste  the  remaining  paste.  Into  what  has  the  starch  been  con- 
verted ? 

26.  To  show  evolution  of  C0%  by  respiration  of  leaves  and 
/lowers,     (f  239. ) 

*  If  several  bubbles  arise  at  once,  remove  shoot  from  water,  dry  the  cut  end  of  Stem 
with  filter  paper  and  coat  it  with  a  thin  layer  of  grafting  wax  ;  then  perforate  thi^  wax 
with  a  line  needle  point  so  a.s  to  offer  one  ail  lot  gases. 


39^  APPENDIX. 

Provide  a  piece  of  plate  glass  and  a  bell  jar  with  ground  rim, 
of  suitable  size  to  cover  a  blooming  plant  growing  in  a  pot. 
Alongside  the  pot  place  a  shallow  dish  of  baryta-water  ;  cover 
both  with  the  bell,  daubing  its  edge  with  vaseline  to  make  con- 
tact with  glass  plate  air-tight.  Place  in  darkness.  Note  film  of 
barium  carbonate  on  surface  of  water  after  a  day.  Conduct  a 
control  experiment,  identical  but  for  the  absence  of  plant.  Is 
more  or  less  barium  carbonate  formed?     Why  darken? 

27.  To  show  evolution  of  CO2  by  respiration  of  seedlings. 

Fill  a  wide-mouthed  glass  jar  or  bottle  of  1  liter  capacity  one- 
third  full  of  peas  and  beans  which  have  been  swollen  for  a  day 
in  water,  then  rinsed  thoroughly  in  5  per  cent,  formalin 
and  again  rinsed  in  water.  Cork  or  cover  tightly.  After  24-48 
hours  remove  cover  and  thrust  in  a  burning  match  or  candle 
attached  to  a  wire.  If  C02  has  been  produced  it  will  extinguish 
flame.  Test  also  by  lowering  into  jar  a  vessel  of  baryta-water. 
If  precipitate  or  film  forms  it  shows  presence  of  C02. 

28.  To  show  the  evolution  of  heat  during  respiration.      (^|  248.) 
Take  three-fifths  the  amount  of  dry  wheat  required  to  fill  two 

3-inch  flower  pots  ;  swell  in  water  over  night ;  rinse  one  half  in  form- 
alin as  above  ;  kill  the  other  by  boiling  in  water  for  five  minutes. 
Stop  bottom  hole  in  pot  with  a  cork;  fill  one  with  dead,  the  other 
with  living  seeds,  and  bring  the  two  to  same  temperature  by  run- 
ning water  through  the  dead  and  hot  one.  Insert  a  thermometer 
in  the  center  of  each  mass  of  seeds  ;  place  both  under  one  box 
or  bell  jar.     Observe  changes  of  temperature  for  two  days.* 

29.  To  measure  the  rate  of  growth  in  length. 

Construct  an  auxanometer  as  follows  :  Take  a  board  30  cm. 
square,  a  common  spool,  a  wheat  or  oat  straw  35  cm.  long,  and  a 
piece  of  glass  tubing  5  cm.  long,  which  will  just  allow  spool  to 
revolve  easily  on  it.  Close  one  end  of  the  glass  tube  by  holding 
it  in  the  flame  of  a  Bunsen  burner  ;  when  hot  spread  it  enough 
to  stop  spool  from  passing  over  end,  by  pressing  it  endwise 
against  a  piece  of  iron.  With  a  fine  saw  cut  a  section  5  mm. 
thick  from  middle  of  spool,  thus  making  a  wheel.  File  a  groove 
in  edge  of  this  wheel,  deep  enough  to  carry  a  thread.  Slip  wheel 
on  glass  tube  and  fasten  it  in  board  near  lower  left  corner  so 
deep  that    spool-wheel   will    revolve    smoothly  but  have   no   un- 

*  Compare  thermometers  previously  to  see  that  they  register  alike ;  if  not  ascertain 
the  correction.  Greater  differences  in  temperature  of  seeds  will  be  observed  if  pots  are 
surrounded  with  cotton  batting. 


DIRECTIOXS  FOR   LABORATORY   STUDY.       399 

necessary  play.  On  the  board,  with  hole  for  glass  tube  as  a 
center,  mark  an  arc  of  90  degrees.  The  radius  of  the  arc  should 
be  a  multiple  of  the  radius  of  wheel.  Divide  arc  into  half  centi- 
meters.    Attach  wheat  straw  to  wheel  as  a  pointer. 

To  the  tip  of  a  growing  seedling  bean  fasten  a  thread  by  a  slip 
noose.  Pass  thread  over  wheel  once  and  to  its  free  end  attach  a 
light  weight — just  enough  to  turn  wheel  and  pointer  when  plant 
is  lifted.  Set  pointer  at  o  and  at  intervals  read  the  multiplied 
growth.  By  taking  observations  at  regular  intervals  determine 
the  rate  of  growth  of  stem  for  a  week.  What  regular  variation 
can  you  discover  ? 

30.  To  show  the  necessity  of  respiration  for  growth.  (^[^[242,  245.) 
Germinate  a  number  of  beans  in  sawdust.     Select  eight  with 

straight  roots  about  2  cm.  long.  Clean  and  dry  the  surface 
slightly  by  brushing  with  frayed  edges  of  strips  of  filter  paper, 
taking  care  not  to  expose  roots  so  long  that  they  are  injured  by 
dry  air.  With  a  very  fine  sablehair  brush  and  thick  Chinese  (or 
waterproof  black  drawing)  ink,  mark  each  root  by  distinct  lines 
into  ten  spaces  1  mm.  apart,  commencing  with  tip.  This  can  be 
done  most  conveniently  by  pinning  the  seedling  to  a  strip  of  soft 
wood  and  laying  alongside  the  root  a  ruler  whose  graduated  edge 
has  been  blunted  by  a  plane  until  it  is  about  2  mm.  thick. 

Pin  half  the  seedlings  to  a  strip  of  soft  wood  set  into  a  jar 
partly  filled  with  wet  sawdust,  so  that  the  roots  will  be  vertical 
in  damp  air.  Put  the  other  half  into  a  similar  jar  and  cover  them 
with  water  recently  boiled  and  cooled.  After  24  hours,  remeasure 
and  compare  total  growth.     (See  also  exp.  31.) 

31.  To  determine  the  zone  of  maximum  growth  in  roots  and  stems. 
(1  258.) 

A.  Observe  the  four  seedlings  of  exp.  30,  whose  roots  grew  in 
moist  air.     Which  spaces  grew  most? 

B.  Mark  several  upper  internodes  of  a  bean  plant  in  a  similar 
way,  but  at  5  mm.  intervals.  After  4S  hours  observe  how  many 
have  elongated  and  which  have  grown  mosti 

32.  To  show  the  effect  of  gravity  as  a  stimulus  on  roots.  ("  *  287- 
290.) 

Arrange  the  marked  root  of  a  seedling  bean  as  in  exp.  30,  ex- 
cept that  the  root  is  horizontal,  and  a  pin  just  above  the  extrem- 
ity murks  its  position.  After  24  hours  observe  curvature  and 
which  spaces  have  become  curved.  Compare  with  those  which 
have  grown  most. 


400  APPENDIX. 

33.  To  show  the  effect  of  gravity  as  a  stimulus  on  growing  regions 
of  upright  leaves  and  items.      (^[^[  2S7-29O.) 

A.  Support  an  onion,  roots  down,  in  a  vessel  of  water  so  that 
it  is  half  immersed,  until  the  leaves  are  about  10  cm.  long.  Then 
turn  it  so  that  leaves  are  horizontal  and  observe  where  curvature 
occurs. 

B.  Cover  the  bottom  of  a  deep  dish  about  25  cm.  long  with  a 
layer  of  wet  sand,  and  bank  this  against  one  end  to  the  top.  Into 
this  bank  stick  horizontally  several  grass  stems  having  at  least 
one  node  ;  cover  with  a  glass  plate.  After  24-48  hours  observe 
curvature.  Cut  a  longitudinal  section  of  the  node  and  observe 
the  part  of  the  leaf-sheath  in  this  curvature. 

34.  To  show  the  effect  of  direction  of  light  as  a  stimulus  on  leaves. 

(IT  285.) 

Set  a  potted  plant  (geranium,  sunflower,  nasturtium,  or  mallow) 
in  the  dark  for  24  hours  ;  then  place  it  before  a  window,  shading 
it  so  that  light  reaches  it  chiefly  from  one  direction.  Mark  certain 
leaves  and  record  the  position  of  the  plane  of  the  blade  ;  24  hours 
later  observe  the  position  and  compare  with  first. 

35.  To  show  effect  of  direction  of  light  as  a  stimulus  upon  stems 
and  roots.     (H  285.) 

Grow  seedlings  of  white  mustard  thus  :  Tie  loosely  over  the 
mouth  of  a  jelly-glass  a  double  piece  of  fine  bobbinnet;  fill  vessel 
with  tap  water  to  the  net,  on  which  place  seeds  ;  set  in  dark,  re- 
placing water  as  it  evaporates,  until  seedlings  are  3  cm.  high, 
with  roots  as  long  or  longer.  Then  place  in  a  box,  blackened 
inside,  into  which  light  is  admitted,  through  a  hole  4-5  cm. 
in  diameter,  at  right  angles  to  stems  and  roots.  Observe  curva- 
tures 24  hours  later. 

36.  To  show  effect  of  intensity  of  light  as  a  stimulus  on  certain 
leaves.     (^[  297.) 

Observe  the  position  of  the  leaflets  of  white,  red,  or  sweet 
clover,  bean,  locust,  or  oxalis  at  3  p.m.,  6  P.M.,  at  dusk  (or  after 
nightfall  by  using  a  lantern)  and  at  8  A.M.  In  the  morning  darken 
with  a  box  a  plant  showing  these  movements.  After  an  hour  or 
two,  observe  the  position  of  leaflets. 

37.  To  show  effect  of  contact  as  a  stimulus  to  tendrils.     (TJ  293.) 
Stroke  with  a  pencil  the  concave  side  of  the  tip  of  a  tendril  of 

passion  vine,  squash,  wild  cucumber,  or  balsam-apple,  on  a  warm 
day  or  in  a  hothouse,  and  observe  curvature  which  follows  in  a 
few  minutes. 


APPENDIX  II. 

DIRECTIONS   FOR   COLLECTING   AND 
PRESERVING    MATERIAL. 

Those  who  cannot  collect  the  plants  they  require  can  orcki  them  from  the  Camhridge 
Botanical  Supply  Co.,  1286  Massachusetts  av.,  Cambridge,  Mass.  Orders  should  be 
placed  in  advance  of  the  collecting  season  to  insure  obtaining  the  material. 

Pleurococcus.  —  For  this  and  similar  one-celled  algae,  collect  pieces 
of  shaded  fence  boards  near  the  ground,  or  flakes  of  bark  from 
the  north  side  of  trees  in  groves  and  parks,  which  show  a  bright 
yellow-green  color.     These  may  be  preserved  dry. 

Oscillaria. — Search  in  drippings  about  watering  troughs,  city 
gutters  where  water  stands,  or  any  open  drain  which  contains 
organic  matter  decaying  in  stagnant  water.  A  glass  jar  or 
aquarium  in  which  water  plants  have  decayed  will  usually  con- 
tain this  plant.  It  may  be  recognized  by  its  bluish  or  blackish 
green  color,  and  often  occurs  in  coherent  films  or  thicker  masses. 
It  may  be  obtained  fresh  at  any  time  of  year,  either  out  doors  or 
in  the  laboratory.  ■ 

Rivularia. — Collect  in  midsummer  or  later  the  larger  water 
plants  to  whose  leaves  and  stems  adhere  jelly-like  lumps  of  a 
dirty  green  color,  from  the  size  of  a  pinhead  to  1-2  cm.  in 
diameter.  The  margins  of  lakes,  pools,  and  slow  streams  furnish 
the  best  localities. 

Nostoc  colonies  form  similar  jelly  masses,  commonly  larger  and 
free  floating  or  attached.       Preserve  both  like  the  following. 

Spirogyra  or  Zygnema. — Search  in  spring  or  early  summer  in  slow 
streams  fed  by  springs.  It  will  be  recognized  when  in  vegetative 
condition  by  rich  green  color  and  slippery  "  feel."  Under  the 
microscope  the    form   of  the   chloroplasts    will   show    the    genus. 

401 


402  APPENDIX. 

(See  1[  25.)      When  conjugating  it  often  loses  the  deep  green  and 
becomes  yellowish,  and  the  filaments  seem  to  be  double. 

This  condition  can  be  recognized  under  the  lens.  Spirogyra 
may  often  be  obtained  all  through  the  year  in  pools  and  springs. 
It  should  De  preserved  in  the  following  solution:  Camphor  water 
50  cc;  water  50  cc;  glacial  acetic  acid  0.5  cc. ;  copper  nitrate 
2  gm.;  copper  chloride  2  gm. 

Cladophora. — Species  of  this  genus  may  be  found  attached  to 
sticks  and  stones  at  the  edge  of  lakes  or  pools.  It  often  covers 
these  completely  with  a  thick  mat  of  long,  yellowish  green, 
branched  filaments.  It  may  be  found  throughout  the  growing 
season.     For  winter  use  preserve  in  same  solution  as  above. 

Chara. — Several  species  are  common  in  shallow  ponds  and  lakes, 
in  water  0.2-1  meter  deep,  rooting  in  the  mud,  often  in  company 
with  Myriophyllum  and  Ceratophyllum,  two  seed  plants,  the  latter 
of  which  may  readily  be  mistaken  for  it  by  novices.  But  these 
plants  are  usually  bright  green  while  Chara  is  dull  or  dirty  green, 
or  even  whitish  (especially  when  dry)  from  the  coating  of  lime, 
which  also  renders  it  brittle  and  harsh  to  the  touch.  Careful  in- 
spection of  its  form  and  a  section  of  the  axis  at  once  enables  one 
to  recognize  it.  (See  figs.  35.  37.)  Specimens  should  be  gathered 
when  the  spermaries  on  the  lower  branches  ("  leaves  ")are  orange. 
Pull  up  the  plants  carefully,  wash  off  as  much  as  possible  of  the 
mud  which  clings  to  the  delicate,  colorless  rhizoids.  The  basal 
part  of  the  axis  should  be  put  in  a  separate  jar  from  the  rest. 
Put  a  few  plants  into  2  per  cent,  chromic  acid,  and  allow  them  to 
remain  24  hours  todissolve  off  lime  with  which  they  are  incrusted. 
After  pouring  off  the  acid  and  rinsing  them  thoroughly,  soak 
them  in  a  large  vessel  of  water  for  24  hours,  changing  water 
several  times  (or  allow  water  to  run  over  them  slowly  for  six 
hours)  to  remove  acid.  Preserve  in  70  per  cent,  alcohol.  Plants 
may  be  preserved  in  formalin  or  70  per  cent,  alcohol,  in  long 
jars  so  as  to  entangle  them  as  little  as  possible.  If  brittle  from 
alcohol  (as  they  often  are)  before  removing  them  from  jar  for 
distribution  pour  off  alcohol  and  cover  with  water  for  a  few 
minutes. 

Polysiphonia. — All  species  are  marine,  and  any  common  species 
will  serve.  They  are  found  in  reddish  brown,  feathery  tufts  2- 
10  cm.  high,  on  other  larger  sea-weeds,  or  on  piles  and  stones, 
about  low-water  mark.  They  collapse  completely  when  with- 
drawn from  the  water. 


COLLECTING   AND    PRESERVING    MATERIAL.  4,0$ 

The  plants  should  be  fixed  in  one  per  cent,  chromic  acid  (or  in  a 
saturated  solution  of  picric  acid  in  sea-water)  for  12-24  hours, 
washed  in  sea-water  as  described  for  Chara,  and  hardened  in  40, 
60  and  80  per  cent,  alcohol  successively,  remaining  in  each  6- 
24  hours.  They  may  be  preserved  in  the  latter.  They  may  also 
be  preserved  in  formalin. 

Fucus. — All  species  are  marine  and  any  one  will  serve.  The 
commonest  is  Fucus  vesiculosus  (fig.  42),  which  may  be  found  on 
rocks  between  tide  marks.  It  is  of  olive-brown  color,  with 
swollen  tips  to  many  of  the  branches,  and  bladders  in  pairs  along 
the  thallus.  Plants  may  be  obtained  fresh  at  almost  any  season. 
Various  species  of  brown  sea-weed  may  be  found  fresh  at  the 
fish  stores  of  all  large  cities,  whither  they  are  sent  as  packing. 

Mucor  or  Rhizopus. — Saturate  a  piece  of  bread  with  water  and 
keep  it  under  a  bell  jar,  in  a  warm  place,  for  a  few  days. 
Several  species  of  molds  will  appear,  the  most  common  of  which 
is  the  black  mold,  Rhizopus  nigricans.  This  may  be  recognized 
by  its  white  fluffy  mycelium,  on  which  arise  tufts  of  erect  hyphae 
developing  at  tips  spherical  sporangia,  at  first  white,  later  black. 
These  tufts  occur  at  intervals  along  a  stolon-like  hypha.  The 
same  mold  may  be  found  on  rotting  vegetables  and  fruits, 
especially  sweet  potatoes  and  lemons,  and  may  be  raised  more 
rapidly  on  bread  by  sowing  spores.  It  will  be  followed  by  the 
green  mold,  Penicillium  glaucum,  and  often  later  by  other 
species.  .  Since  the  plants  may  be  grown  promptly,  the  material 
used  should  be  living. 

Microsphaera  or  Uncinula  or  Erysiphe. — Any  species  of  mildew 
will  answer.  Microsphara  grows  everywhere  on  the  leaves  of 
the  cultivated  lilac.  Erysiphe  is  abundant  on  the  leaves  of  blue 
or  white  vervain  {Verbena  hastata  and  V.  urticafolia)  and  many 
Compositae.  Uncinula  attacks  leaves  of  many  willows.  About 
midsummer,  when  the  fungus  has  a  white  powdery  aspect,  gather 
leaves  and  dry  them  under  light  pressure.  Later,  gather  leaves 
of  the  same  species  showing  yellow  and  black  dots  (the  fruits)  on 
the  mycelium.      Preserve  in  the  same  way. 

Cystopus  portulacae.  —  This  species  is  abundant  throughout  the 
summer  on  leaves  and  stems  of  purslane  (Portulaca  oleracea) 
which  grows  in  every  garden  and  cornfield.  Another  s; 
grows  in  late  spring  on  shepherd's-purse  (Cipse//,i  bursa-pastoris) 
and  another  on  the  pigweeds  (AmarantAus  sp.).  Anyone  will 
answer.      The    species  on    Capsella  (Cystopus  candidus)  only   oc- 


404  APPENDIX. 

casionally  forms  resting  spores  in  that  host.  They  may  be  found 
in  abundance  in  the  flowers  of  radish  which  become  much  enlarged 
and  distorted  when  this  fungus  is  parasitic  thereon.  All  species 
may  be  known  by  the  white  blisters  formed  by  lifting  the  skin  of 
the  host.  Preserve  in  formalin  or  alcohol  leaves  and  stems  of 
host  bearing  blisters.     Some  may  also  be  dried. 

Peziza. — The  cup  fungi  grow  on  earth  or  fallen  rotting  leaves, 
twigs  or  trunks,  in  woods.  The  fructifications  may  be  at  once 
recognized  by  their  cup-like  form.  The  inner  surface  of  the  cup 
is  often  bright  colored,  red  or  orange,  brown  or  black.  The 
mycelium  is  hidden  in  the  substratum.  They  may  be  collected  in 
spring  and  summer  and  preserved  in  formalin  or  70  per  cent, 
alcohol. 

Lichens.  —  Any  common  foliose  species  which  forms  apothecia 
abundantly  will  answer.  A  bright  gray  species  with  black  apo- 
thecia (Physcia  stclluris)  is  abundant  on  tree  trunks,  as  is  also  a 
yellowish  species  with  orange  apothecia  {Theloschistes  polycarpa). 
These  may  be  collected  at  any  convenient  time,  and  kept  dry. 
Besides  these,  collect  other  foliose  forms;  also  species  of  Cladonia 
growing  on  the  ground,  with  body  much  lobed  and  the  apothecia 
coral-red  knobs  on  upright  gray  stalks;  also  species  of  Ustiea, 
clothing  the  branches  of  trees  with  gray-green  shrub-like  or  hair- 
like tufts. 

Mushroom. — Any  species  with  cap  and  gills  will  answer.  They 
may  be  found  in  woods  throughout  the  summer  and  especially 
in  late  summer  or  autumn  during  a  rainy  season  following 
drought.  Only  the  fructification  need  be  collected.  Select  a 
small  firm  species  with  well  defined  stalk,  cap  and  gills.  Col- 
lect fructifications  in  all  stages  of  development  from  young  to 
mature.  Preserve  as  soon  as  gathered  in  formalin  or  70  per  cent, 
alcohol. 

Other  Hymenomycetes. — Collect  fleshy  cap  fungi  with  hanging 
points  instead  of  gills  {Hydnum,  fig.  217),  or  intersecting  plates 
forming  tubes  {Boletus).  Preserve  these  as  mushroom.  Collect 
also  the  woody  bracket  fungi  (Polyporus,  fig.  218),  which  grow  on 
rotten  trees  and  fallen  limbs,  showing  innumerable  fine  tubes 
underneath.  Preserve  dry.  Also  the  much  branched  firm- 
fleshed  Clavaria  (fig.  215).  Preserve  as  mushroom.  All  will  be 
found  in  damp  woods. 

Marchantia. — Common  on  wet  ground  and  rocks,  or  even  in 
drier    places  among  grass  in   the  shade  of  walls  or  fences.      It 


COLLECTING   AND    PRESERVING    MATERIAL.  405 

may  be  recognized  by  flattish  green  body  about  1  cm.  wide  and 
5-8  cm.  long,  attached  by  silky  hairs.  At  some  times  it  bears  on 
the  upper  surface  sessile  cups  containing  green  grains,  and  sends 
up  erect  slender  sexual  branches  which  spread  out  into  flat  heads 
6-8  mm.  across,  some  scalloped  at  edge  and  some  with  finger-like 
rays.  When  cups  or  sexual  branches  are  present  no  other  liver- 
wort can  be  mistaken  for  it.  A  very  similar  one,  except  in  these 
parts  (Conocephalus  conicus)  may  be  distinguished  by  its  larger 
size  and  larger  stomata,  looking  like  needle  pricks  over  the  sur- 
face, while  those  of  Marchantia  are  just  visible.  It  may  be  used 
for  the  vegetative  parts.  Collect  in  July.  Free  from  dirt  as 
much  as  possible,  and  preserve  in  formalin  or  70$  alcohol. 

Porella. — Abundant  everywhere  on  the  bases  of  trees  especially 
in  low  grounds  or  wet  bottom  lands.  It  may  be  recognized  by 
its  dirty-green  pinnately  branched  shoots,  1-2  mm.  wide,  with 
crowded  overlapping  rounded  leaves.  The  plants  are  always  in- 
tricately interwoven.  Flakes  of  the  bark  may  be  peeled  off  with 
a  broad  knife  or  chisel,  taking  care  not  to  tear  up  the  plants  into 
too  small  patches.  Collect  in  summer.  Preserve  dry,  after  dry- 
ing under  light  pressure.  Some  should  be  kept  in  formalin  or 
alcohol  for  demonstration  of  finer  structure  of  sex  organs. 

Mnium. — Any  species  of  the  genus  will  do.  The  commonest 
species  eastward  is  M.  cuspidatum.  It  is  abundant  everywhere  in 
patches  on  shady  banks  and  in  open  woods  about  the  bases  of 
trees.  It  may  be  recognized  by  the  yellow  or  orange  oval  cap- 
sule, thin  and  irregularly  wrinkled  when  dry,  horizontal  or  pen- 
dent on  a  stalk  2-3  cm.  long.  The  leaves  are  broadly  oval,  with 
fine  sharp  teeth  under  lens,  and  a  distinct  midrib.  When  moist 
the  leaves  are  rather  pale  green,  ahd  not  crowded  or  overlapping. 
When  dry  the  clump  is  a  dull,  dirty  green,  and  the  leaves  are 
much  curled  and  twisted,  expanding  quickly  when  wetted.  The 
male  and  female  organs  are  in  the  same  cluster,  at  the  apex  of 
the  axis.  Under  the  microscope  the  species  may  be  recognized 
by  the  oraitgt-  inner  peristome  with  double  rows  of  perforations 
in  the  membrane  below  the  segments.  Preserve  as  directed  fur 
Porella.  Almost  any  similar  moss  will  serve  equally  well,  espe- 
cially the  common  species  of  Bryum, 

Equisetum. — The  gametophytes  are  not  readily  obtainable.  The 
sporophytes  of  the  common  E.  arvinse  grows  on  dry  sandy  banks, 
often  on  railroad  embankments.  The  underground  stems  send 
up  in  spring  (April-May)  unbranched  flesh  colored  shoots  5  mm. 


406  APPEXDIX. 

in  diameter  and  10-25  cm.  high,  with  brown  scale-like  sheaths  at 
the  nodes.  These  shoots  terminate  in  a  cone-like  cluster  of 
sporophylls.  Later  in  the  season  from  the  same  underground 
stems,  grow  green  much  branched  shoots,  looking  somewhat  like- 
miniature  pines,  the  main  lateral  axes  being  produced  in  whorls 
at  the  nodes.  Collect  both  sorts  of  aerial  shoots  with  under- 
ground shoots  and  roots  attached.  Preserve  the  flesh-colored 
and  underground  shoots  and  a  few  green  shoots  in  alcohol  or 
formalin  ;  most  of  the  green  shoots  may  be  dried  under  light 
pressure  between  drying  paper  or  newspaper. 

Adiantum. — Gametophytes  of  any  fern  will  answer.  They  are 
flat  green  heart-shaped  bodies  2-5  mm.  in  diameter,  attached  to 
soil  by  rhizoids.  They  may  be  collected  on  fern  pots  or  grown 
in  greenhouses,  or  may  be  obtained  from  supply  company  named. 
Especial  care  should  be  taken  to  have  some  young  sporo- 
phytes  still  attached  to  gametophytes.  The  sporophytes  of 
the  maidenhair  fern  are  easily  recognized  by  the  peculiarly 
branched  leaf.  The  stem  is  wholly  underground.  Each  leaf 
has  a  slender  polished  stalk  which  forks  into  two  equal 
branches  ;  these  fork,  one  branch  of  each  pair  growing  straight 
and  bearing  leaflets  while  the  other  again  forks  in  the  same  way  ; 
and  so  on  until  4-8  branches  have  been  formed  on  each  half. 
Collect  underground  stems  and  roots,  loosening  them  gently  and 
washing  off  dirt  carefully  to  avoid  destroying  all  root  tips  and 
hairs.  Preserve  these  in  alcohol  or  formalin.  Gather  leaves 
when  the  crescent-shaped  fruit  dots  at  edges  of  leaflets  are  yel- 
lowish brown  (August).  Preserve  by  drying,  spreading  out 
each  leaf  to  show  its  mode  of  branching  clearly. 

Selaginella. — A  wild  species',  S.  rupestris,  grows  abundantly  on 
dry  bare  hills  and  rocks.  It  forms  grayish-green,  much  branched 
tufts,  3-8  cm.  high,  with  narrow  bristle-tipped  appressed 
leaves,  and  resembles  in  aspect  a  large  rigid  moss.  Many 
branches  are  terminated  by  a  sharply  quadrangular  spike  of 
sporophylls,  about  1  cm.  long.  Several  exotic  species  are  com- 
monly cultivated  in  greenhouses  and  window  gardens,  where 
they  produce  sporangia  abundantly.  Any  species  will  answer. 
Collect  the  wild  plant  about  July.  Specimens  may  be  preserved 
dry  or  in  alcohol  or  formalin. 

Pinus. — Any  species  will  answer.  The  Scotch  pine  is  so  widely 
planted  that  it  is  often  easiest  to  collect.     The  leaves  are  grayish 


COLLECTING   AND    PRESERVING    MATERIAL.  API 

green,  in  pairs,  5-10  cm.  long;  cones  small,  about  5  cm.  long, 
the  ends  of  scales  bearing  a  conspicuous  protuberance,  long  and 
recurved  on  the  basal  scales.  The  Austrian  pine,  also  widely 
planted,  has  dark  green  longer  leaves  (10-15  cm-)»  larger  cones, 
with  no  recurved  bosses.  The  flowers  are  of  two  sorts  and 
should  be  watched  for  in  spring  (May)  as  new  shoots  appear. 
The  staminate  flowers  form  conspicuous  yellow  clusters  at  the 
base  of  the  young  shoots,  and  should  be  collected  as  soon  as  the 
sporangia  begin  to  shed  the  spores.  The  pistillate  flowers  are 
quite  inconspicuous,  small  oval  clusters  (5-7  mm.  long)  pro- 
jecting slightly  beyond  the  tip  of  the  young  shoots.  The  tree 
bearing  staminate  flowers  usually  bears  few  pistillate  ones,  and 
vice  versa.  Collect  shoots  bearing  each  kind  of  flowers,  cutting 
far  enough  back  to  include  the  leaves  of  the  previous  year.  Pre- 
serve in  alcohol  or  formalin.  Collect  also  year-old  and  two-year- 
old  cones.  Preserve  the  former  (green)  in  fluid;  the  latter 
(mature)  dry. 

Caltha. — This  plant  is  common  in  wet  meadows  and  swamps 
northward.  It  is  15-30  cm.  high,  smooth,  with  rather  coarse 
hollow  ribbed  stems,  orbicular  or  kidney-shaped  alternate  leaves, 
with  broad  clasping  base  to  the  petiole,  and  numerous  bright 
yellow  flowers  20-25  mm.  in  diameter,  produced  for  two  weeks 
or  more  in  April  or  May.  Gather  entire  plant;  wash  the  roots. 
Preserve  a  few  plants  and  an  extra  supply  of  flowers  and  fruits 
in  alcohol  or  formalin.      Dry  most  of  the  entire  plants. 

Lathyrus. — The  sweet  pea  is  grown  in  almost  every  flower  gar- 
den and  is  known  everywhere.  Preserve  flowers  and  leaves  in 
summer  in  alcohol  or  formalin. 

Stems. — The  various  sorts  recommended  may  be  collected  at 
any  convenient  time  and  preserved  in  fluid. 

Seeds. —  The  nmsi  useful  seeds  for  laboratory  work  are  Indian  corn, 
wheat,  buckwheat,  castor  bean  (  Ricinus),  white  lupine,  {Lupinusal- 
dus),  scarlet  runner  (Phaseolus),  broad  bean  {Vicia  faba),  hemp, 
white  mustard.  These  should  be  obtained  fresh  each  year,  as  they 
deteriorate  more  or  less  with  age.  Those  which  cannot  be  had 
everywhere  (such,  perhaps,  as  lupine,  castor  bean,  scarlel 
runner,  and  broad  bean)  may  be  purchased  of  seedsmen  in  Large 
cities.      See  advertisements  in  magazines. 

Potted  plants. — Such  as  arc  grown  in  window  gardens  or  all 
greenhouses    will  suffice.     A  commercial  greenhouse,  if  accessi- 


408  APPENDIX. 

ble,  will  raise  tomato,  castor-bean,  bean,  and  sunflower  plants  as 
ordered,  and  will  furnish  active  young  plants  at  any  season  re- 
quired, in  case  pupils  cannot  grow  them  either  at  school  or  home. 
Malt. — Can  be  obtained  ground  or  unground  at  any  brewery, 
or  may  be  made  by  sprouting  barley  until  the  seedlings  appear 
and  then  drying  at  about  ioo    C. 


APPENDIX  III. 
APPARATUS   AND   REAGENTS. 

The  chemicals  required  are  so  few  that  in  most  cases  they 
may  be  most  conveniently  obtained  through  local  dealers.  It  is 
desirable,  however,  to  order  apparatus  from  dealers  who  make  a 
specialty  of  manufacturing  or  supplying  optical,  chemical,  and 
physical  apparatus.  Schools  are  entitled  to  import  such  appara- 
tus free  of  duty,  and  by  doing  so  through  importing  firms  a  large 
part  of  the  cost  may  be  saved.  The  list  is  given  here  for  its 
convenience  as  a  summary.  The  amounts  necessary  are  not 
specified  as  they  vary  with  the  size  of  classes,  and  the  teacher 
who  is  prepared  to  conduct  the  experiments  can  readily  deter- 
mine how  much  is  needed. 

CHEMICALS. 

Acetic  acid. — Used  for  fixing  protoplasm. 

Alcohol. — Large  schools  should  buy  in  barrel  lots  free  of  reve- 
nue tax.  For  regulations  apply  to  the  revenue  collector  of  the 
district  in  which  the  school  is  situated,  or  to  the  Secretary  of  the 
Treasury. 

Ammonium  hydrate  (ammonia). 

Barium  hydrate, — For  making  baryta  water;  or  this  can  be  ob- 
tained fresh  as  needed  from  druggist. 

Chromic  acid.  —  Used  in  fixing  and  decalcifying. 

Corn  starch. — As  prepared  for  table  or  laundry. 

Formalin. — This  is  a  40  per.  cent  solution  of  formaldehyde  in 
water.  Dilute  solutions  can  be  prepared  as  needed.  Mosl 
plants  require  a  10  per  cent  solution,  i.e.,  formalin  1  part,  water 
9  parts. 

Grafting    7cax.  —  Made    as    follows  :     Melt     together     resin    (by 

409 


4IO  APPENDIX. 

weight)  4  parts,  beeswax  2  parts,  tallow  i  part;  mix  well;  pour 
into  a  pail  of  cold  water;  grease  the  hands  and  "  pull "  till  nearly 
white.  In  using  it  should  be  handled  with  greased  fingers  to 
prevent  its  sticking  to  them. 

Iodine.  —  Either  solid,  from  which  the  tincture  can  be  prepared 
by  dissolving  a  few  flakes  in  alcohol,  or  the  tincture  may  be  pur- 
chased. 

Mercury. — For  directions  for  keeping  it  clean  and  dry,  see 
Botanical  Gazette  22  :   471.     Dec.  1896. 

Paraffin. — A  common  quality,  melting  at  about  650  C. 

Phenolphtalein. — A  few  grams  will  last  a  long  time. 

Potassic  hydrate. — May  be  bought  in  sticks  and  the  solution 
made,  but  it  is  more  convenient  to  buy  the  liquor  potasses  of 
druggists. 

Sodium  chloride. — Table  salt  is  pure  enough. 

Vaseline. 

APPARATUS  FOR  MORPHOLOGY. 

Dissecting  microscopes. — Each  pupil  should  be  provided  with  one. 
A  most  effective  low-priced  dissecting  microscope  was  designed 
by  the  author  and  is  manufactured  by  several  firms.  In  no  case 
has  the  author  any  financial  interest  in  the  instruments.  The 
stand  T  I,  manufactured  by  the  Bausch  &  Lomb  Optical  Co., 
Rochester,  N.  Y.,  with  i-inch  lens,  and  a  similar  one  by  Queen 
&  Co.,  Philadelphia,  have  been  approved  by  the  designer.  Many 
forms  offered  to  schools  by  jobbers  are  not  worth  buying. 

Compound  microscopes. — The  school  should  be  supplied  with  at 
least  one  good  compound  microscope  for  demonstrations,  and  as 
many  more  as  can  be  profitably  used.  If  the  teacher  is  capable 
of  using  such  instruments  properly  he  will  be  able  to  select  it 
wisely  with  such  advice  as  he  may  obtain  from  personal  acquaint- 
ances on  whose  judgment  he  can  rely.  Schools  are  advised  to 
deal  only  with  manufacturers  of  established  reputation. 

Scalpels.  —  Each  pupil  should  be  provided  with  a  sharp  knife 
with  slender  blade  for  dissection.  It  is  desirable  for  the  school 
to  furnish  scalpels  of  suitable  form.  The  slender  blades,  3-3.5 
cm.  long  on  cutting  edge,  are  recommended. 

Forceps. — Straight  form,  with  smooth  points,  will  be  found  use- 
ful, though  not  indispensable. 

Needles.  —  Each    pupil  should  have   a   pair   of    needles   (No.   6, 


APPARATUS   AND    REAGENTS.  41  I 

sharps)  with  the  eye  end  set  into  a  soft  pine  penholder  or  similar 
handle.     They  must  be  kept  sharp  on  a  fine  oil-stone. 

Drawing  mad-rials. — A  medium  pencil  (No.  3  or  M)  and  a  very 
hard  one  (No.  6  or  6  H)  should  be  used  and  kept  sharp.  Slips  of 
heaviest  linen  ledger  paper  (120  lb.)  cut  14  X  8  cm.  are  recom- 
mended.    Only  one  drawing  should  be  put  on  a  slip. 


APPARATUS  FOR  PHYSIOLOGY. 

Since  much  of  the  apparatus  needs  to  be  put  together  by  the 
student,  the  requisites  are  mainly  tools  and  a  good  supply  of  tub- 
ing, both  glass  and  rubber,  bottles,  and  bell  jars.  The  following 
will  enable  the  foregoing  experiments  to  be  carried  out. 

Tools. —  Hammer,  fine  saw,  three  or  four  chisels,  assorted  files, 
brace  and  assorted  bits,  screw-driver,  smoothing  plane,  with  a 
supply  of  nails  (especially  finishing  nails)  and  screws  will  be 
found  most  useful. 

Glass  tubing. — A  little  capillary  tubing  (0.5  mm.  bore)  will 
be  needed.  Most  used  sizes  are  5  mm.  (3  mm.  bore),  7  mm. 
(5  mm.  bore.)  Some  larger  sizes  (13  and  19  mm.)  will  also  be 
useful. 

Rubber  tubing. — 3  and  5  mm.  bore  mostly  ;  some  of  10  and  15 
mm.  bore. 

Bottles. — Wide-mouthed,  various  sizes,  up  to  1  liter. 

Tumblers. — Jelly  glasses  answer  well.  Odd  lids  and  glass  dishes 
from  homes  and  stores  can  be  made  useful. 

Corks. — Assorted  sizes.  Several  rubber  stoppers,  sizes  S,  10,  12, 
3-hole,  are  desirable. 

Bell  Jars. — Several  sizes  are  necessary  ;  1;  X  20  and  20  X  30  cm. 
will  be  found  useful;  also  at  least  one  30  X  50  1  in.  All  should 
have  ground  rim  and  tubulure  at  top. 

Funnels. — Glass,  assorted  sizes.  <>,  8,  and  u  cm.  diam.  are 
most  used  ;  there  should  also  be  two  or  three  larger  ones. 

filter  paper. — Buy  cut  filters  15  and   iS  cm.  in  diameter. 

Thermometers. — Should  be  graduated  in  degrees,  — io°  to -f- ioo° 
C,  with  milk-glass  scale. 

Test  tubes. — 2  X  15  cm.  is  a  convenient  size. 

T -tubes. — Two  sizes.  5  and  10  mm.  bore. 

Bunsen  burners.  —  If  gas  is  not  available,  gasolene  burners 
should  be  substituted. 


412  APPENDIX. 

Marble-. — A  plate  25  X  25  X  2.5  cm.,  polished  on  both  sides.  It 
can  be  re-polished  after  etching  and  used  as  often  as  desired. 

Filter  pump. — Can  be  used  if  water  service  is  available,  or  if  a 
head  of  5  m.  can  be  secured  by  tank.      Korting's  is  excellent. 

Rulers. — 30  cm.  long,  graduated  in  millimeters. 

Brushes. — Camelhair  brush  of  large  size,  and  sablehair,  smallest, 
are  useful. 

Pius. 

Tin  tube. — 3  X  15  cm.     See  experiment  20. 

Absorbent  cotton. — Also  a  roll  of  cotton  batting. 

Sheet  lead. — Light  weight,  used  by  plumbers. 

Plate  glass. — Cut  into  pieces  20,  25,  and  35  cm.  square. 

Pine  sawdust  and  clean  sand. — For  germinating  seeds. 


APPENDIX  IV. 
REFERENCE  BOOKS. 

The  following  books  will  be  found  useful  to  teacher  or  pupil  or 
both,  and  are  recommended  as  suitable  reference  books  for  the 
school  library.  The  list  is  not  intended  to  be  exhaustive,  nor 
does  it  include  books  for  popular  reading. 

FOR   GENERAL    REFERENCE. 

Kerner:  Natural  history  of  plants.  New  York:  Henry  Holt  & 
Co.     $15.00.     (Translated  by  Oliver.) 

Strasburger,  Noll,  Schenck  and  Schimper  :  Text-book  of 
botany.  New  York  :  The  Macmillan  Co.  $4.50.  (Trans- 
lated by  Porter.) 

Bennett  and  Murray  :  Handbook  of  cryptogamic  botany.  New 
York:  Longmans,  Green  &  Co.     $5.00. 

Vines  :  A  student's  text-book  of  botany.  New  York  :  The  Mac- 
millan Co.     $3.75. 

Sachs  :  Lectures  on  the  physiology  of  plants.  New  York  :  The 
Macmillan  Co.     $7.00.     (Translated  by  Ward.) 

Goebel  :  Outlines  of  classification  and  special  morphology.  NY  w 
York  :  The  Macmillan  Co.  $5.50.  (Translated  by  Garnsey 
and  Balfour.) 

Warming:  Handbook  of  systematic  botany.  New  York:  The 
Macmillan  Co.     $3.75.     (Translated  by  Potter.) 

Gray  :  Systematic  botany.  New  York  :  The  American  Book  Co. 
$2.00. 

Bessey  :  Botany,  Advanced  Course.  New  York  :  Henry  Holt  & 
Co.     $2.20. 

Geddes  :  Chapters  in  modern  botany.  New  York:  Charles 
Scribner's  Sons.     $1.25. 

413 


414  APPENDIX. 

Warming:  Lehrbuch  der  iikologischen  Pflanzengeographie.  Ber- 
lin: Gebr.  Borntrager.  (A  German  translation  by  Knoblauch. 
An  English  translation  is  now  in  preparation.) 

PfeFFER  :  Pflanzenphysiologie.  Ed.  II.,  vol.  I.  Leipzig:  Wil- 
helm  Engelmann.  M.  20.  (An  English  translation  is  now  in 
preparation  by  Dr.  A.  J.  Ewart.) 

Vines  :  Lectures  on  the  physiology  of  plants.  New  York  :  The 
Macmillan  Co.     $5.00. 

Goodale  :  Physiological  botany.  New  York:  The  American 
Book  Co.     $2.00. 


FOR   LABORATORY   DIRECTIONS. 

Bergen:  Elements  of  botany.     Boston:  Ginn  &  Co.     $1.10. 

Spalding  :  Introduction  to  botany.  Boston  :  D.  C.  Heath  &  Co. 
80  cts. 

Macbride  :  Lessons  in  elementary  botany.  Boston :  Allyn  & 
Bacon.     60  cts. 

MacDougal  :  Experimental  plant  physiology.  New  York  :  Henry 
Holt  &  Co.     $1.00. 

Arthur  :  Laboratory  exercises  in  vegetable  physiology.  Lafay- 
ette, Ind.:   Kimmel  &  Herbert.     (Pamphlet.)     35  cts. 

Darwin  and  Acton  :  Practical  physiology.  New  York  :  The 
Macmillan  Co.     $1.60. 

Arthur.  Barnes  and  Coulter  :  Plant  dissection.  New  York  : 
Henry  Holt  &  Co.     $1.20. 


APPENDIX  V. 
OUTLINE   OF   CLASSIFICATION. 

In  the  foregoing  work  no  endeavor  has  been  made  to  present 
any  scheme  of  classification,  but  only  to  develop  certain  principles 
in  logical  fashion.  As  a  supplement  the  following  general  classi- 
fication, adapted  mainly  from  Strasburger,  Noll,  Schenck  and 
Schimper's  Lehrbuch  der  Botanik,  may  be  useful  in  showing  the 
relationship  of  the  more  important  plants  named  in  the  text  and 
appendices. 

All  classification  is  more  or  less  artificial.  The  purpose  of  such 
an  outline  is  to  indicate  roughly  the  present  knowledge  of  kinship 
among  plants.  Even  were  knowledge  perfect  it  would  naturally 
be  impossible  to  do  this  in  a  linear  arrangement  such  as  is  neces- 
sary in  a  book.  Moreover,  knowledge  is  far  from  complete.  It 
is  to  be  expected,  for  example,  that  ultimately  botanists  will  be 
able  to  express  much  more  accurately  the  relationship  between 
the  groups  of  fungi  and  the  algae  than  is  now  possible.  Then, 
the  various  groups  of  fungi  will  be  ranked  alongside  the  green 
plants  to  which  they  are  most  akin,  as  is  now  done  in  the  Schizo- 
phyta,  instead  of  being  constituted  a  class  by  themselves. 

The  following  classification  differs  more  or  less  from  all  others 
in  details.  Like  them,  it  is  merely  tentative,  and  will  be  modified 
as  knowledge  increases.  Only  in  the  most  general  divisions  will 
all  schemes  be  found  similar. 

Subkingdom  I.     THALLOPHYTA.     Thallophytes. 

Class  I.  Myxomycetes.     Slime  molds. 
Class  II.   Schizophyta.      Fission  plants. 

Order  I.   Schizophycece.      Fission  alga?.      Blue-green  algae. 

Nostoc.     Rivularia.     Oscillaria. 
Order  2.     Schitomycetes.     Fission  fungi. 
Bacteria. 

415 


416 


APPENDIX. 


Class  III.  Diatomeae.     Diatoms. 

Class  IV.  Peridineae.     Often  ranked  as  animals. 

Class  V.   Conjugate.      Brook  silks  and  desmids. 

Spirogyra.     Zygnema.     Mesocarpus.     Desmids. 
Class  VI.  Chlorophyceae.     Green  algae. 
Order  I.  Protococcales. 

Pleurococcus.     Volvox. 
Order  2.    Cottfervoidales.     Confervoid  algae. 
Ulothrix.     Cladophora.      Ulva. 
Order  3.   Siphonales. 

Vaucheria.     Caulerpa.     Acetabularia. 
Class  VII.   Phaeophyceae.     Brown  algae. 
Order  1.   Phaosforales.1 

Lessonia. 
Order  2.   Fucales.1 

Fucus.     Sargassum. 
Order  3.   Dictyotales. 
Class  VIII.   Rhodophyceae.     Red  algae. 

Orders  numerous.      Polysiphonia. 
Class  IX.  Characeae.     Stoneworts. 
Chara.     Nitella. 
Class  X.  Hyphomycetes.     True  fungi. 

A.   Phycomycetes.     Algoid  fungi. 


Heterogamous  Series. 
Sub-class  I.    Oomycetes. 
Orders     numerous.     Cys- 
topus. 


B.   Mesomycetes. 
Sporangiate  Series 
Sub-class  III.    Hemiasci. 
Yeast. 

C.   Mycomycetes 
Sporangiate  Series. 
Sub-class  V.   Ascomycetes. 
Witch-broom  fungus.      Mil- 
dews.    Truffles.      Penicil- 
lium.   Cup-fungi.   Morels. 
Class  XI.  Lichenes.     Lichens. 

Physcia.     Theloschistes 
1  Various  larger  species  known  as  tangles,  kelp,  r 


Isogamous  Series. 
Sub-class  II.   Zygomycetes. 
Orders  numerous. 

Mucor.   Rhizopus.   Em- 
pusa. 
Intermediate  fungi. 

Non-sporangiate  Series. 
Sub-class  IV.   Hettribasidii. 
Brand  fungi.     Smuts. 
Higher  fungi. 

Non-sporangiate  Series. 
Sub-class     VI.     Basidiomy- 

cetes. 
Rusts.       Cap-fungi.      Poly- 
porei.     Puff-balls. 


.k-weed,  bladder-wratk. 


OUTLINE    OF   CLASSIFICATION.  417 


Subkingdom  II.     BRYOPHYTA.     Bryophytes.     Mossworts. 

Class  I.   Hepaticae.      Liverworts. 
Order  1.   Ric  dales. 

Riccia. 
Order  2.   Marchantiales.     Liverworts. 

Marchantia.      Lunularia. 
Order  3.   Anthocerotales.     Horned  liverworts. 
Order  4.  Jungermanniales.    Leafy  liverworts.    Scale  mosses. 

Porella. 
Class  II.  Husci.     Mosses. 

Order  1.   Sphagna  Us.     Peat  mosses. 

Sphagnum. 
Order  2.  Andreaales. 
Order  3.   Archidiales. 
Order  4.  Bryales.     True  mosses. 

Bryum.     Mnium.      Hypnum. 


Subkingdom  III.     PTERIDOPHYTA.     Pteridophytes. 
Fernworts. 

Class  I.  Filicineae. 

Order  1.   Filicales.     True  ferns. 

Adiantum.      Pteris.     Aspidium.     Asplenium. 
Order  2.   Hydropteridales.     Water  ferns. 
Class  II.   Equisetineae.     Horsetails.     Scouring  rushes. 

Equisetum. 
Class  III.  Lycopodineae. 

Order  1.   Lycopodiales.     Ground  pines. 

Lycopodium. 

Order  2.   Selaginellales.     Club  mosses. 

Selaginella. 


Subkingdom  IV.     SPERMATOPHYTA.     Seed  plants. 


Class  I.  Gymnospermae.     Gymnosperms. 
Order  1.   Cycadales.     Cycads. 
Cycas. 


41 8  APPENDIX. 

Order  2.    Coniferales. 

Pines,  spruces, larches,  firs,  etc. 
Order  3.   Gnetales. 

Welwitschia. 
Class  II.   Angiospermae.     Angiosperms. 

Sub-class  I.   Monocotyledon.es.     Monocotyledons. 

Orders    several.      Lilies,    irises,    grasses,    sedges,    rushes, 
palms. 
Sub-class  II.   Dicotyledones.     Dicotyledons. 

Orders    numerous.       Most    herbs   with    net-veined    leaves, 
deciduous  shrubs  and  trees. 


INDEX. 

All  references  are  to  pages.  When  there  are  two  or  more  references  to  the 
same  topic,  figures  in  bold-face  indicate  the  definition  or  chief  discussion  of  the 
subject.     Italic  figures  indicate  illustrations. 


Absorption,  carbon  dioxide  165  ; 
water  74,  153,  155,  323 

Acacia,  leaves  I :  't 

Acetabularia  23,  l'4 

Achillea,  inflorescence  257 

Achlya,  sex  organs  293 

Acids,  carbon  175 

Adaptations  146,  308 

Adiantum  382;  embryo  62,  68; 
leaf  126;  spermary  282 

Aeration  171 

Agaricus  377,  404 

Agrimonia,  fruit  866 

Ailanthus,  fruit  864 

Air,  distributing  seeds  363;  dis- 
tributing spores  356;  effect  of 
composition  312  ;  effect  of 
moisture  in  316;  -plants  152 

Alcanna,  corolla  250 

Aldrovandia  ..'}>: 

Aleurone  grains  169 

Algae,  eggs  ?86,  288;  fission  8; 
gametes  278;  imprisoned  338, 
877 ;  in  other  water  plants  33  1 

Alkaloids  177 

Allium,  stem   106 

Aloe,  epidermis  828 

Alternation  of  generations  49. 
60 

Amanita,  fructification  219 

Amorpha,  sleep  movement  .'".v 

Amorphophallus,  leaf  125 

Anabaena  10 

Anabolism  166 

Anagallis,  fruit  SOS;  pistil  :','> 

Anaptychia,  apothecium 


Angiosperms   237;    ovary    291; 

seed  299;  sperr.iary  281 
Animals,   and    plants   336,    338, 

342;    distributing    seeds    365; 

distributing  spores  357 
Anther  246 

Anthyllis,  venation  137 
Ants  and  plants  348 
Apical  cell,  Cha.ra.SO,  31;  Funis 

34',  liverworts  51;  Polysipho- 

nia  32;  root  67,  6S;  shoot  84 
Apodanthes  S40 
Apogamy  294 
Apparatus  409 
Apple,  fruit  S05 
Arbor  vitae,  shoot  97 
Archegonium  289 
Arisarum,  flower 
Armor,  protective  347 
Artemisia,  hail 
Ash,  pistil  of  .;/ 
Asparagus,  branches  92 
Aspidium,     pinnule    280;    s.irus 

281;  sporangium 
Asplenium,  buds   262;  gamete* 

phyte  60 
Assimilation  1 62 

Astragalus,  pistil 
A  ulai  omnium,  brood  bud 
Automatism  u^.  188 
Auxanometer  isn 

Bai  tei  ia  to,  //.  12 
Bacterium  aceti  // 
Balsam,  stem  6 
I  tai  berry,  thori 

,19 


420 


INDEX. 


Bark  111,  116 

Bast,  secondary  113 

Bazzania  53 

Bean,  geotropic  roots  199,  201 

Beech,  mycorhiza  336 

Beet,  stoma  184 

Begonia,  stem  bundle  104 

Bellflower,  fruit  802;  leaf  ro- 
sette 196 

Bidens,  fruit  367 

Bird's-nest   fungus  218 

Blackberry  305 

Bladderwort  343.  344,  345 

Blade,  leaf  123;  structure  of 
leaf  133 

Blasia  54 

Boletus  404 

Books,  reference  413 

Bracts  131,  236,  256 

Branches,  dwarf  90,  91,  92 

Branching  22;  of  leaves  122, 
124,  125,  126,  128,  138;  of  liv- 
erworts 51;  of  mosses  57;  re- 
production by  267;  of  root  78; 
of  shoot  86;  of  stamens  249 

Brood  buds  260 

Bryony,  tendril  94 

Br  yum,  capsule  58,  228,  280; 
section  of  stem  56 

Buckthorn,  leaf  128 

Buds,  85,  88;  adventitious  89; 
axillary  87;  dormant  89;  on 
roots  81;  reproductive  263; 
shoot  85 

Budding  40,  211,  267 

Bulb  90,  326 

Bulblets  93 

Bundles,  vascular  71,  72,  100, 
103,  114,  132,  136 

Butomus,  anther  248 

Butternut,  buds  88 

Cactus,  forms  98 

Calamus,  root  72 

Caltha  389.  407 

Calyptospora,  haustoria  ^5; 
spores  854 

Calyx  237,  253 

Campanula,  fruit  302;  leaf  ro- 
sette 196 

Canna,  leucoplasts  4 


Capsella,  embyro  66;  pistil  242 

Carbohydrates  159;  manufac- 
ture 166 

Carbon  dioxide,  absorption  165 

Carex,  leaf  edge  348 

Carnivorous  plants  342 

Carpels  235,  236,  237 

Carpogonium  287 

Carrot,  chromoplasts  6 

Caulerpa  23,  24,  25 

Cecropia,  stem  349 

Cedar,  gametophytes  284 

Cell  1;  division  17,  18;  naked 
147;  wall  5 

Centrifuge  199 

Centrospheres  4 

Cereus,  shoot  98 

Chara27,  2S,  30,2,11,  402;  ovary 
281;  spermary  2S0,  881 

Characeae  27 

Cheiranthus,  hairs  101 

Chelidonium,  hair  cell  191 

Chemotaxis  274 

Cherry,  cork  cambium  110; 
fruit  304 

Chlorophyll,  function  166;  spec- 
trum 166,  16? 

Chloroplasts  4,  5,  21;  move- 
ments 192 

Chondromyces,  colonies  884 

Chromoplasts  5 

Cilia  12,  147,  190 

Cinchona,  bark  112;  stem  108 

Cinnamon,  flower  248 

Cladonia  377 

Cladophora  22,  28,  .'./,  370,  402 

Cladophylls  92 

Classification  415 

Clavaria,  fructification  219,  404 

Claviceps,   fructification   /.'.       ' 

Climate,  relation  of  plants  to 
308 

Climbers  330 

Close-pollination,  adaptations 
for  358 

Clover,  root  tubercles  337 

Club-mosses,  sporangia  231 

Clusia,  periderm  of  root  74 

Cobsea,  flower  360 

Cockle-bur,  fruit  367 

Ccenocytes  22 


JXDEX. 


421 


Cohesion,  carpels  241;  stamens 
248 

Cold,  protection  against  315 

Colonies,  gelatinous  8 

Color,  significance  359 

Conducting  tissues  156 

Cone,  pine  998 

Conifers,  fruit  29S 

Conjugatae  16,  20 

Conjugation  269,  274 

Contact  movements  203 

Contractility  145 

Convolvulus,  hairs  321 

Coprinus,  gill  217 

Cosmos,  stamens  249 

Cotton,  fruit  366 

Cotyledons  117 

Cork  110;  cambium  no 

Corm  90 

Corn,  stem  bundles  107 

Cornus,  inflorescence  257 

Corolla  237,  253 

Coronilla.  sleep  movement  207 

Cortex,  Chara  30;  leaves  135; 
root  72,  73;  secondary  109; 
stem  100,  109 

Cranberry  rust,  spore  chain  354 

Crataegus,  stipules   121 

Cross-pollination  255;  adapta- 
tions for  358 

Crucibulum  21S 

Crystals  175,  176,  351 

Cup  fungus  223 

Currant,     nectary    177;    ovules 

Cuscuta  889 

Cutin  6 

Cuttings  266 

Cycas,  carpel  238;  seed  897 

Cystocarps,   Polysipbonia    988, 

£89 
Cystopus  277,  375,  403 
Cytoplasm  2 

Dandelion,  fruit  866 

Datura,  anther  248;  leaf  mo- 
saic 196 

Dehiscence,  anthers  247;  fruit 
301,  80S,  808 

Development,  phases  of  178 

Desmids  16 


Desmodium  fruit  366 

Diatoms  14,  16 

Dichotomy  78,  86 

Digestion  162;  intracellular  170 

Dionaea  346;  leaf  208,  34-5 

Distribution,   of    seeds    361;  of 

spores  353 
Dodder  889 

Dogwood,  inflorescence  257 
Domatia  350 
Dorsiventrality  57 
Draba,  hairs  822 
Dracaena,  stem  114 
Drosera,  leaves  345 
Duration,  of  root   73;  of  shoot 

94 

Echinocactus,  shoot  98 

Ecology  144,  307 

Edelweiss,  hairs  321 

Eel  grass,  runners  265 

Egg  285 

Elaeagnus,  scales  322 

Elaters  7,  355 

Elatine,  stem  102 

Elder,  lenticel  US 

Elm,    buds  88;    cork   cambium 

110 
Emergences  101,  102,  802 
Embryo  62,  63,  66,289,291,  295, 

296,   297,   300,   304;    sac    243, 

244 
Empusa  354 
Endodermis,   root    72,     75,    77; 

stem  100,  115 
Endosperm  298,  299 
Energv,  released  by  respiration 

173  ' 
Entoderma  in  alga 
Enzymes  162 
Epidermis,  adaptations  320;  of 

leaf  133;  of  root  70;   of  stem 

100,  101 
Epipactis,  cell  division  17 
Epiphytes  331 
Epispore  214 
Equisetum  230,  282,  384;  apical 

bud  8Jt;  sporangium  wall  988) 

spore- 
Ergot,  fructification  .;?. 
Erysiphe  924,  375;  f™'1 


422 


INDEX. 


Eschscholtzia,  ovules  243;  pro- 
tection of  stamens  353 
Excretion  173 
Exobasidium  43 

Fagus,  mycorhiza  &?<? 

Fats  160 

Fennel,  resin  receptacle  176 

Fermentation  162 

Fern,  maidenhair  3S2,  406 

Fernworts  60;  ovary  290;  sper- 
mary  280,  282;  sporangium 
229,  356 

Fertilization  255,  285 

Fig,  inflorescence  260 

Filament  246 

Fir,  seed  297;  seedling  118 

Fission   17,  211 

Flax,  stem  104 

Flower  92,  236;  leaves  131; 
movements  196 

Fly  fungus  354 

Fly  trap,  leaves  208,  345 

Foliage  119 

Food, for  insects  359;  insects  as 
342;  with  spores  215 

Foods  159;  manufacture  166, 
16S;  storage  16S;  transloca- 
tion 168 

Fossombronia  54 

Fragmentation  211 

Fraxinus,  pistil  241 

Freezing,  protection  against 
315 

Fructifications  218 

Fruits,  accessory  304;  adapta- 
tions to  distribution  of  seed 
361;  of  angiosperms  300;  dry 
300;  fleshy  303,  3(17;  of  gym- 
nosperms  298;  multiple  305 

Fucus  33,  34,  373,  4°3;  egg  286; 
ovary  287,  288;  spermary  278 

Funaria,  leaf  56;  development 
of  sporophyte  206;  ovary  290 

Function  143;  limits  to  146;  unit 
of  144 

Fungi  39,  213,  216  ff.,  335,  337, 
338;  fission  10;  loss  of  sex- 
uality 293 

Fusion,  of  hyphae  45;  of  sta- 
mens 249 


Gametophyte  49;  of  fernworts 
60;   of  liverworts  58,  54;  of 

mosses  55;  reduction  61,  292; 
of  seed  plants  64;  shoot  82 

Gaultheria,  fruit  S04 

Gelatin  6,  12 

Gemmae  260 

Geotropism  197 

Gerardia,  parasitic  SS9 

Germination,  adaptations  to 
367;  of  pollen  251 

Glceocapsa  S 

Grafting  267 

Grain  301 

Grasses,  geotropic  node  199, 
200;  lea.H20;  rolling  of  leaves 
S19 

Grimmia,  capsules  855 

Growth  151,  178;  conditions  of 
183;  daily  period  1S5;  dura- 
tion 187;  grand  period  1S1 ; 
induced  295;  intercalary  38; 
of  leaves  137,  138;  localiza- 
tion of  22;  measuring  180; 
movements  due  to  192;  of  cell 
wall  7;  of  spores  215;  region 
of  181;  spontaneous  varia- 
tions in  1S7 

Gymnosperms  237;  ovary  291; 
seed  297;  spermary  280,  282 

Hairs  320,  821,  822,  347;  absorb- 
ing 323;  glandular  360;  of 
stem  101 

Halophytes  311,  326 

I  laustoria  45,  46 

Heat  from  respiration  174 

Heatli,   rolled  leaf  821 

Heliotropism  194 

Hellebore,  pistil   .' :}  1 

Helotism  333,  337 

Heterocysts  9 

Heterogamy  271,  276 
Hibernacula  204 
Honeysuckle,   buds  SS;    leaves 

128 
Hop,  emergences  202 
Horse-chestnut,  leaf  126 
Horsetails  384,  405;    sporangia 

230,    232;     sporangium    wall 

§88;  spores  ..;.; 


INDEX. 


423 


Host  161 

Houseleek  S25 

Hydnum,  fructification  220,  404 

1  [ydrophytes  311,  327 

Hydrotropism  202;  apparatus 
SOS 

II ylocomium  56 

Hyphse  39;  branching  40;  fu- 
sion 45 

Indian  turnip,  inflorescence  256 
Infection  with  fungi  43 
Inflorescence  S7 
Insects,  adaptations  of  flowers 

to    358;    distributing     spores 

357;  exclusion  of  359;  as  food 

342 
Integuments,   of  ovule    243;   of 

seed  299 
Internodes  96;  of  Chara  27 
Involucre  256 

Irregularity  254;   purpose  359 
Irritability    145,    183,    188,    274; 

localization  189 
Isogamy  271,  274 
Ivy,  chloroplasts  4 

Katabolism  170,  175 

Land  plants  152,  311 

Larch,  gametophyte  282,  283; 
shoot  320 

Lasiagrostis,  rolling  of  leaf  S19 

Lathyrus  407 

Leaves,  adaptation  314,  320; 
arrangement  119;  base  120; 
blade  123;  development  117; 
fall  of  140;  form  119;  growth 
137.  138;  of  mosses  57;  origin 
53;  pine  91,  92;  primary  117; 
secondary  117;  stalk  122; 
structure  132,  189;  suppres- 
sion 319;  as  water  recepta- 
cles 324 

Leguminosfe,  root  tubercles  336 

Lenticels  113 

Leucoplasts  .'/,  5 

Lichens   J'.,  47,  .'.'.7,  337 

Light,  effect  on  growth  [84, 
185;  effect  on  form  313;  effect 
on  water  plants  33S;  escaping 


319;   produced  by  plants  17c 

relation  to  photosyntax  166 
Lignification  6 
Lily,  anther  .'/,S;  buds  262 
Lime,  effect  of  317 
Linden,  domatia  350;  shoot  86 
Liverwort  49,  378,  379,  404,  405; 

sporangium  227 
Locomotion  190 
Locust,     development    of     leaf 

139;  stipule  thorns  ISO 
Lodgers  334 
Lonicera,  buds  S8 
Lotus,  fruit  SOS 
Lunularia  %9,  50 
Lychnis,  petal  254;  stigma  2j0 
Lycopodium,  stem  103 

Malt  40S 

Maple,  buds  88;  fruits  S24;  leaf 
188;  mosaic  195 

Marchantia  378,  404;  elaters  7 
rhizoids  7;  spermarv  979 
thallus  267;  brood-buds  262 
thallus  261 

Marigold,  marsh  389,  407 

Marsilia,  root  tip  68 

Mechanical  tissues  149;  devel- 
opment of  1S6 

Mechanics  of  body  149 

Megasporangium  234 

Megaspore  231;  of  lily   .' 

Melampsora,  spore  beds  215 

Meristem,  primary  35;  of  root 
68;  of  shoot  84;  secondary  74, 
108 

M>s, 1,  arpus     21;      conjugating 

Mesophytes  311,  312 
Metabolism  145,  215 
Metzgeria  ■'•-' 
Micrococcus  // 
Microsphaera  375,  403 
Microsporangium  234 
M  i<  rospores  231 

Mildew  :."/.   375,  403;  fru  • 

Milkweed,    Bowers   252;  pollen 

mass 
Mimicry  3  p 

Mimosa,  leaves  208;  sleep 
movement  ."-, 


424 


INDEX. 


Mineralization   7 

Mnium  381,  405 

Moisture,  effect  on  growth  186 

Monopodial  branching,  of  root 
7S;  of  shoot  87 

Monostroma  26 

Monotropa,  pollen  tube  283 

Morchella,  fructification  286 

Morning  glory,  chloroplasts  4; 
seedling   US 

Mosaic,  leaf  195,  106 

Mosses  53,  3S1;  brood  buds.?'/'.'; 
sporangium  229;  teeth  355; 
sporophyte  822 

Mossworts,  ovary  289;  sper- 
mary  2S0 

Motor  organs  192,  295 

Mountain  ash,  chromoplasts  6 

Mousetail,  flower  259 

Movements  188;  combined  196; 
contact  203,  207;  for  entrap- 
ping animals  345;  of  water, 
effect  on  plants  328;  para- 
tonic  193;  photeolic  206;  spon- 
taneous 193,  206;  to  protect 
spores  352 

Mucor  41,  403;  sporangium  222 

Mulberry  306;  flower  and  fruit 
305 

Mushroom  377,  404;  gill  SI? 

Mustard  seedlings, geotropic/.%? 

Mutualism  333 

Mycelium  41 

Mycorhiza  335,  336 

Myosurus,  flower  259 

Nectar  176;  guides  to  359 

Nectaries  177 

Nemalion,  ovary  288 

Nettle  hair  348 

Nitella  27,  ."■> 

Nitrogen,  supply  342 

Nodes  96;  of  Chara  27 

Nostoc  9,  369,  401 

Noteroclada  54 

Nucleus  3 

Nutation  193 

Nutrition  151;  of  Oscillaria  10 

Oats,  cell  from  leaf  4;  epider- 
mis 134 


Odor,  cause  176;  purpose  359 

Offsets  90,  265 

Oils  176 

Oleander,  leaf  824 

Oleaster,  scales  822 

Oligotrichum,  leaf  56 

Onion,  embryo  56;  stem  106 

Oogonium  287 

Opuntia  321 

Orange,  oil  receptacle  177 

Orchid,  chromoplast  6;  light 
seeds  363;  mycorhiza  886 ; 
pollen  tube  283 

Organ  143 

Origin  of  roots  79 

Orthotrichum,  branching  57 

Oscillaria  10,  370,  401 

Osmosis  156 

Ovary  240,  273,  286 

( Hulury  240 

Ovules  237,  242,  243,  244;  dia- 
grams 285 

Oxalis,  cells  102 

Oxygen,  effect  on  growth  186; 
supply  171 

Pansy,  seed  300 

Parasites  43,  161,  163 

Parasitism  333,  338 

Parmelia,  thallus  825 

Pea,  flower  255;  growth  of  root 
182  ;  leaf  tendrils  130  ;  root 
branches  79;  sweet  407 

Pellia,  sperms  280 

Peperomia,  water  storing  326 

Pepper,  fruit  800 

Perennials  in 

Perianth  236,  252 

Pericarp  300;  adaptations  to 
distribution  of  seeds  3(12 

Pericycle,  root  71  ;  stem  100, 
103' 

Periderm,  root  74,  75;  second- 
ary in;  stem  109 

Perisperm  29S,  299 

Peronospora,  haustoria  46;  sex 
organs  87? 

Petal  237 

Petiole  122;  scarlet  runner  105', 
sensitive  128;  structure  132 

Peziza  223,  376,  404 


INDEX. 


425 


Phascum,  sporophyte  59 
Phaseolus,    motor    organs   905; 

stele  of  root  75,  76 
Phelloderm  109 
Phloem,    bundle    of    root    72  ; 

secondary  109 
Photosyntax   166;  product    167; 

and  respiration  171,  175 
Phycocyanin  8 
Phycoerythrin  33 
Phycophaein  3S 
Phyllodia  I:', 
Phyllotaxy  119 
Physcia  376,  404 
Physiology  143;  apparatus  411; 

experiments  391 
Phytolacca  seed  300 
Pilobolus,  abjection  of  sporan- 
gium S5S 
Pilularia,  megaspore  214 
Pimpernel,  fruit  SOS;   pistil  £45 
Pine  387,  406;  carpel  238;    cone 

298  ;  shoot   91  ;    wood,   pene- 
trated by  hyphae  44 
Pineapple  306 
Pine  sap  988 
Pistil  237;  diagram  £85;  simple 

and  compound  240 
Pitcher  plants  129,  342,  S48 
Pitfalls  342 

Pith,  rays  115;  stem  107 
Placenta  244 
Plasmodia  14S 
Plastids  4 

Plectranthus,  hairs  101 
Pleurococcus  13,  369,  401 
Pokeberry, seed  SOO 
Pollen,    grains  249,    250  ;    tube 

."/",  281,  ?8S,  ?84,  886 
Pollination  255,  358 
Polyembryony  294 
Polygonatum,  leaf  VB7 
Polygonum,     megaspore 

Stipules   /.'./;   tubers  U) 
Poly  podium  61 
Polyporus     4.!  ;      fructification 

i£0,  404 
Polysiphonia    31,    St,    372,    402; 

cystocarps     $88,    £89  ;    tetra- 

s pores  .'.',' 
Folytrichum  55 


Pondweed,  hibernacula  268 

Poplar,  mycorhiza  335 

Poppy,   ovules  243;   protection 

of  stamens  353 
Porella  379,  405 
Potassium     salts,     relation     to 

photosyntax  167 
Potato,    pistil    241  ;    starch    5  ; 

seedling    ?66 
Pressure,  effect  on  growth  186; 

root  156 
Prickles  101,  K/J,  347 
Proteids  160;  grains  169;  manu- 
facture 168 
Prothallium  60 
Protonema,  mosses  58 
Protoplasm  2;  movements   191; 

naked  147;  powers  145 
Psychotria,  domatia  350 
Pteris,   embryo   62  ;    origin    of 

root  SO;  ovary  290 
Puff  ball  214,  221 
Putrefaction   162 
Pyrenoids  21 
Pyrola,  fruit  302 

Radiolarian  and  algae  33S 

Rainfall,  adaptations  to  316 

Ranunculus,  leaf  120;  nectary 
177 

Raspberry  305 

Reaction  189 

Reagents  409 

Rejuvenescence  268 

Repair  151 

Reproduction  145,  209;  adapta- 
tions 352;  sexual  268;  vegeta- 
tive 211 

Resins  176 

Respiration  171;  intramolecular 
172 

Rheum,  flower  .">■'' 

Rhizoids  22;  Chara  31;  liver- 
worts 50;  mosses  53 

Rhizome  90 

Rhizopus  374,  403 

Rhododendron,  anthers  and 
pollen   . '/.'' 

Riccia  50 

Rigidity,  how  secured  149 

Rings,  annual,  of  stem  116 


426 


INDEX. 


Rivularia  369,  401 

Robinia,  thorns  ISO 

Root  65;  adaptations  156;  ad- 
ventitious 267  ;  aerial  324  ; 
cage  200,  201;  cap  68,  70,  71; 
climbers  331  ;  differences 
from  shoot  85  ;  fleshy  77  ; 
float  77;  hairs  69,  70;  hairs 
and  soil  154;  hairs,  solvent 
action  155;  origin  from  leaves 
139  ;  parasitic  889  ;  pressure 
156;  pressure,  apparatus  for 
157;  primary  65;  secondary 
67  ;  tap  324  ;  tendrils  78  ; 
thorns  7S  ;  tubercles  336  ; 
woody  76 

Rose,  flower  260;  leaves  122  ; 
prickle  102;  seedling  IIS 

Rotation  of  protoplasm  191 

Runner  90,  265 

Rye,  daily  period  of  growth 
185;  stem  IS  4 

Sage,  anther  247 
Salts  in  water  154,  164 
Salvinia,  sporangium  285 
Saprolegnia,  zoospores  213 
Saprophytes  161 
Sarcina  11 
Sargassum  37,  38 
Saxifrage,  flower  360 
Scales  320,  322;  leaf  130 
Scarlet    runner,  motor    organs 

205 
Scions  266 

Scutellaria,  cortex  109 
Secretion  receptacles  176, 177 
Sedge,  leaf  edge  848 
Sedum,    flower  .'/..',   259;  offsets 

.<•■; 

Seed   296,  407;  in   angiosperms 

299;  distribution  306,  361;  in 
gymnosperms  297 

Seed  plants,  ovary  290  ;  para- 
sitic 340  ;  spermary  280  ; 
spores  and  sporangia  234 

Selaginella  386,  406  ;  female 
gametophyte  291  ;  male  ga- 
metophyte  282;  stem  105 

Selection,  power  of  164 

Sempervivum  826 


Sepal  238,  253 

Sex  organs  273 

Sexuality,  imperfect  269;  loss 
of  293;  origin  268 

Shepherd's  purse,  embryo  66; 
pistil  242 

Shoot  82;  differences  from  root 
S5;  from  leaves  139;  liver- 
worts 52;  primary  83 

Sleep  movements  206 

Soil  153;  effect  of  temperature 
of  315  ;  effect  of  physical 
characters  317;  limits  of  ab- 
sorption from  155  ;  salts  in 
154;  water  in  154 

Solutions,  water  152 

Spadix  256 

Spathe  256 

Spermary  274,  277 

Sperms  276 

Sphseroplea,  gametes,  286 

Sphagnum,  sporophyte  228 

Spirogyra  20,  370,  401  ;  conju- 
gating 272 

Splachnum,  capsules  58 

Sporangia  216,  221;  of  anther 
247;  of  fern  356 

Spore  212;  chains  217;  diagram 
216;  germinating  4-:  '<  non- 
sexual 212;  of  Penicillium 211 ; 
of  Filularia  214;  protection 
352;  resting  294;  sexual  268 

Sporophylls  131,  230 

Sporophyte  49,  227,  292;  fern- 
worts  62;  mosses  58,  59,  :::; 
shoot  83;  seed  plants  64 

Spruce,  ovaries  284 

Stamens  235,  236,  245 

Starch,  manufacture  167  ;  re- 
serve 169 

Stem  96;  climbing  99;  erect  98 
forms  of  xerophytic  319;  o 
mosses  55,  56;  prostrate  98 
sections  99,  102,  108,  104,  105 
106,  108,  114;  shape  97;  struc 
ture  99;  twining  99 

Stele,  of  leaves  136;  of  root  71; 
of  stem  100,  103 

Stigma  240 

Stimulus  188;  transmission  of 
190 


INDEX. 


427 


Stipules  121 

St.  John's  wort,  stamens  250, 
251 

Stolon  90 

Stomata  134;  sunken  322 

Stonecrop,  flower  259;  offsets 
264 

Storage  107;  of  foods  168,  169; 
in  leaves  131;  in  roots  77 

Strawberry,  flower  258,  259; 
runners  264 

Streaming  of  protoplasm  191 

Style  240 

Suberin  6 

Sugar,  manufacture  167  ;  re- 
serve 169 

Sugar  cane,  epidermis  323 

Sundew,  leaves  345 

Suspensor  66,  291 

Symbionts  161 

Symbiosis   161,  333 

Symphoricarpus,  fruit  cells  179 

Sympodial  branching,  in  moss 
57;  in  shoot  of  seed  plants  86 

Syrrhopodon,  brood  buds  262 

Telegraph  plant,  leaf  206 
Temperature,  effect  on  growth 

185;  on    form   314;    on  water 

plants  328 
Tendril,  of  bryony  94;  leaf  130; 

movement  of  203;  shoot  93 
Tension,      distributing      seeds 

362;  distributing  spores  355; 

of  tissues  149,  182 
Tetragonolobus,    sleep     move- 
ments 207 
Tetrasporangia,       of        Polysi- 

phonia   .'.',' 
Thallus  22,  25;  of  Fucus  34;  of 

liverworts  49 
Thickening,  secondary,  of  root 

74,  77;  of  stem  107,  115 
Thlaspi,  leaf  VSS 
Thorn  apple,  anther  248 
Thorns  347;   leaf  130;  shoot  93; 

of  Veil  a  96 
Thyme,  anther  247 
Tococa,  base  of  leaf  350 
Torus  236,  258 
Traction,  effect  on  growth  186 


Trametes  44 
Transfer  of  foods  168 
Transpiration   158;  adaptations 

for  reducing  318 
Traps  343 

Trefoil,  fruit  of  tick  $66 
Tropaeolum,  leaf  128 
Tubers  93,  326 
Turgor  148;  distributing  seeds 

362;  distributing  spores  353; 

movements  204 
Twiners  201,  331 
Tylanthus,  leaf  321 

Ulothrix   21;  reproduction  270, 

271;  zoospores  269 
Ulva  26 
Uncinula  403 
Urtica,  hair  348 
Utricularia  343,  344,  345 
Uvularia,  leaves  128 

Vacuoles  2,  179 

Vallisneria,      distribution       of 

spores  356,  857;  runners  265 
Vanda,  light  seeds  868 
Vanilla,  leucoplasts  5 
Varnish,  on  epidermis  321 
Vascular    bundles    71,    72,   100, 

103,  114,  132,  136 
Vaucheria  22,    23  ;    sex  organs 

278 
Vella,  thorns  95 
Venation,  leaves   125,  127,  137, 

13S 
Veratrum,  pistil  .'.;/ 
Vicia,  vascular  bundles  of  root 

75 
Violet,  anther  2 40;  fruit /.v.' 

Water,  absorption  153,  323  ; 
distributing  seeds  362;  dis- 
tributing spores  356  ;  effect 
of  composition  329;  effect  of 
movements  32S;  force  raising 
157;  loss  158;  movement  150; 
necessity  152  ;  path  of  156  ; 
percentage  151  ;  -plants  152, 
327;   salts  in  K14;  storing  325 

Waste  products  175 

Wax,  on  epidermis  321 


428 


INDEX. 


Weight,  loss  of  173 
Welwitschia  140 
Willow,  fruit  S65;  leaf  127 
Wind,    distributing    seeds  363; 

distributing  spores  356;  effect 

on  form  313 
Wings  to  fruits  364 
Wintergreen,  fruit  302,  304 
Wheat,    flower  258;    geotropic 

stem  200;  seedling  11S 
Wood,  in  root  71;  secondary  113 

Xanthium,  fruit  367 


Xerophytes  311,  318 
Xylern  bundles,  of  root  72;  sec 
ondary  109 

Yarrow,  inflorescence  257 

Yeast,  beer  40 

Yew  ovule  and  fruit  239 

Zamia,  flower  233 
Zea.  stem  bundles  107 
Zoospores  i^T,  212 
Zygnema  20,  401 


"Should  find  a  place  in  every  college  and  pubtic  library." — Boston  TRANSCRIPT. 

KERNER'S  NATURAL  HISTORY 
OF   PLANTS. 

Translated  by  Professor  F.  W.  Oliver,  of  University  College, 
London.  A  work  for  reference  or  continuous  reading,  at  once 
popular  and,  in  the  modern  sense,  thoroughly  scientific.  *  With 
16  colored  plates  and  iooo  wood  engravings.  Four  parts.  4to. 
Cloth.     $15.00  net. 

The  Nation  ;  "  The  author  evidently  planned  at  the  outset  to  take  every  attractive 
teature  of  plants  of  all  grades,  and  place  these  attractive  features  in  the  very  best  light. 
For  this  purpose  he  has  skillfully  employed  a  brilliant  style  of  exposition,  and  he  has  not 
hesitated  to  use  illustrations  in  black  and  in  color  with  the  freest  hand.  The  purpose  has 
been  attained.  He  has  succeeded  in  constructing  a  popular  work  on  the  phenomena  of 
vegetation  which  is  practically  without  any  rival.  The  German  edition  has  been  accepted 
from  the  first  as  a  useful  treatise  (or  the  instruction  of  the  public  ;  in  fact,  some  of  its  illus- 
trations have  been  taken  bodily  from  the  volumes  by  museum  curators,  to  enrich  exhibi- 
tion cases  designed  for  the  people.  With  two  exceptions,  the  full-page  colored  plates 
leave  little  to  be  desired,  and  might  well  find  a  place  in  every  public  museum  in  which 
botany  has  a  share.  Most  of  the  minor  engraving* are  unexceptionable.  They  are  clear, 
and  almost  wholly  free  from  distracting  details  which  render  worthless  so  many  iflusl  ra- 
tions in  popular  works  on  natural  history.  Professor  Kerner's  style  in  German  is  seldom 
obscure — it  is  what  one  might  fairly  call  easy  reading;  but  it  i-  no  disparagement  to  him 
and  his  style  tostale  that  the  translation  is  clearer  than  the  origin.il  throughout.  .  .  In  the 
first  two  issues  the  author  was  engaged  chiefly  with  thestudy  of  thestructureof  the  plant, 
and  its  adaptation  to  itssurroundings.  In  this  concluding  volume  he  considers  the  plant 
from  the  point  of  view  of  its  relation  toothers.  Therefore  he  begins  with  a  full  and  ab- 
sorbingly interesting  account  of  reproduction  in  the  vegetable  kingdom,  and  then  passes  to 
an  examination  of  species.  .  .  With  this  book,  there  is  no  excuse  for  even  busy  people  to 
be  ignorant  of  how  the  other  half,  the  plant-half,  lives." 

Botanical  Gazette  :  "  Kerner's  work  in  English  will  do  much  toward  bringing  modern 
botany  before  the  intelligent  public.  We  need  more  of  this  kind  of  teaching  that  will 
bring  those  not  professionally  interested  in  botany  to  some  realization  of  its  scope  and 
great  interest  " 

Professor  J.  E.  Humphrey:  "  It  ought  to  sell  largely  hereto  colleges  and  public  libra- 
ries, as  well  as  to  individuals,  and  lean  heartily  commend  it." 

John  1/.  Afac/arlane,  Professor  in  University  of  Pennsylvania  :  "  It  is  a  work  that 

deserves  a  wide  circulation." 

Professor  John  M.  Coulter  in  The  Dial :  *'  It  is  such  books  as  this  that  will  bring 
botany  fairly  before  the  public  as  a  subject  of  absorbing  interest  ;  that  will  illuminate  the 
botanical  lecture-room  ;  that  will  convert  the  Gradgrind  of  our  modern  laboratory  into  a 
student  of  nature." 

New  York  Times  :  "  A  magnificent  work,  with  its  careful  text  and  superb  illustrations 
The  whole  processof  plant  life  is  explained,  and  all  the  wonders  of  it." 

The  Critic:  "  In  wonderfully  accurate  but  easily  comprehended  descriptions,  it  open 
to  the  ordinary  reader  the  results  of  botanical  research  down  to  the  present  time." 

The  Outlook  :  ".  .  .  For  the  first  time  we  have  in  the  English  language  a  great  work 
upon  the  living  plant,  profound,  in  a  sense  exhaustive,  thoroughly  reliable,  but  in  language 
simple  and  beautiful  enough  to  attract  a  child.  .  .  The  plates  are  most  of  them  of  unusual 
beauty.  Author,  translator,  illustrators,  publishers,  have  united  to  make  the  work  a 
success." 

HENRY  HOLT  &  CO.,  29  West  23d  Street,  New  York. 


SCIENCE 
REFERENCE  AND  TEXT-BOOKS 


rriu.isiiKi)  »v 


HFNRY  HOLT  &  COMPANY,  2' 


New  Yokk 


Books  marked  *  are  chiefly  for  reference  an  J  supplementary  use,  and  are 
to  be  found  in  Henry  Holt  &*  Co.1  s  List  of  Works  in  General  Literature. 
For  further  particulars  about  books  not  so  marked  see  Henry  Jlolt  cV  Co,yS 
Descriptive  Educational  Catalogue.  Excepting  James's  PSYCHOLOGIES, 
Walker's  Political  Economies,  and  Adams'  Finance,  all  in  the  Ameri- 
can Science  Series,  this  list  contains  no  works  in  Philosophy  or  Economics. 

Smcrican  Science  Series 

1.  Astronomy.      BySlMON  Nrwcomb,  Professor  in  the  Johns  Hopkins  University, 

and  Edward  S.  HoLDKN.late  Director  of  the  Lick  Observatory,  California, 

Advanced  Course.     512  pp.     8vo.     $2.00  net. 
The  same.     Briefer  Course.     352  pp.     12010.     $1.12  net. 
The  same.    Elementary  Course.    By  E.  S.  HoLDEN.    446  pp.    121110.     $i.2o»<-/. 

2.  Zoology.    By  A. S.  Packard,  Jr.,  Professor  in  Brown  University.   Advanced 

Course,      j-22  pp.      8vo.      $2.40  net. 
The  same.      Briefer  Course.     338  pp.     $1.12  net. 
The  Same.     Elementary  Course.     290  pp.      12m  >.     80  cents  net. 

3.  Botany.     By    C.    E.    Bhssey,    Professor     in     the    University    of    Nebraska. 

Advanced  Course.     611  pp.     8vo.     $2.20  net. 
The  same.     Briefer  Course.     356  pp.     $1.12  net. 

4.  The  Human  Body.     By  H.  Nkwbll  Martin,  sometime  Professor  in  the  Johns 

Hopkins  University. 

Advanced  Course.     6S5    pp.     8vo.     $2-50  net.     Copies   without  chapter  on 

Reproduction  sent  when  specially  ordered. 
The  same.    Briefer  Cows,-.    {Entirely  new  edition  revised  ry  Prof.  C.  Wells 

Fitz.  op  Harvard.)     408  pp.      i2ino.     $1.20  net. 
The  same.     Elementary  Course.     261pp.     nmo.     75cents«.j'. 
The  Human  Body  and  the  Effect  of  Narcotics.     261  pp.     umo.     $1.20  net. 

5.  Chemistry.      By     Ika    Rbmsbn,     Professor    in     Johns     Hopkins     University. 

Advanced  Course.     850  pp.     8vo.     $2.80  net. 
The  same.     Briefer  Course.     435  pp.     $1.12  net. 
The  same.     Elementary  Course.     272  pp.     12010.     80  cents  net. 
Laboratory  Manual  (to  Elementary  Course).     io6pp.     121110,    40  cents  net. 
Chemical  Experiments.     By   Prof.   Rbmsbn  and   Dr.  W.   W.  Randal!..     (For 

Briefer  Course.)    No  blank  pages  for  notes.     158  pp.    12DJO.     50  Cents  net. 

6.  Political  Economy.     By  Franc  is  A.  Walker,  President  Massachusetts  Insti- 

tute of  Technology.     Advanced  Course,    537  pp.    8vo.     82-00  net. 
The  same.     Briefer  Course.     415  pp.     i2mo.     $1  ao  net. 
The  same.     Elementary  Course.     423  pp.     121110.     $1.00  net. 

7.  General  Biology.     By  Prof.   w.  t.  Sbdcwick,  of  Massachusetts  Institute  of 

Technology,  and  Prof.  K.  if.  Wilson,  of  Columbia  College.    (Revised  and 
enlarged,  1896.)    231  pp.    8vo.    $1.7,  net. 

8.  Psychology.      By  Wniiwt  Jambs,  Professor  in  Harvard  College.     A.: 

Course.     689  +  704  pp.     8vo.     2  vols.     $4.80  net. 
The  same.     Briefer  Course,     478  pp.     lamo.     $1  to  net. 

9.  Physics.      By  GBORG1  F    BaRKBR,  Professor  in  the  University  of  Pennsylva- 

nia.    Advanced  Course.    902  pp.     8vo.     $}.y>  net. 

10.  Geology.     By  Thomas  C.  Chambbrlin  and  Rolun  D.  Salisbury,  Professor* 

in  the  University  of  Chicago.     ( In  Preparation.) 

11.  Finance.      By  Henry  Carter  Adams,  Professor  in  the  University  of  Michi- 

gan.    Advanced  Course,     xiii  +  573  pp.     8vo.     $3.50  net. 
.11,1900  (l) 


HENRY  HOLT  &    CO.'S  WORKS   ON  SCIENCE. 


Allen's    Laboratory  Exercises   in    Elementary  Physics.       By  Chas.    R. 

Allen,  of    the    New    Bedford,    Mass.,    High    School.     Pupils' 

Edition,  x  -f  209  pp.,   80c,  net.      Teachers'  Edition,  $1.00,  net. 
Arthur,  Barnes,  and  Coulter's  Handbook  of  Plant  Dissection.     By  Prof. 

J.  C.  Arthur,  of  Purdue  Univ.,   Prof.  C.  R.  Barnes,  of   Univ. 

of   Chicago,    and    Pres.   John   M.    Coulter,   of    Lake    Forest 

Univ.     xi  +  256pp.     §1.20,  net. 
Atkinson's    Elementary    Botany.     By    Prof.    Geo.    F.    Atkinson,    of 

Cornell.     Fully  illustrated,     xxiii  -f-  441  pp.     %\.2$,  net. 
Atkinson's  Lessons  in  Botany.     Illustrated.     365  pp.     $1.12,  net. 
Barker's  Physics.     See  American  Science  Series. 

Barnes's  Plant  Life.  By  Prof.  C.  R.  Barnes,  of  University  of 
Chicago.      Illustrat.d.     x  -f  428  pp.     $1.12,  net. 

Barnes's  Outlines  of  Plant  Life.     Illustrated.     308  pp.     $1.00,  net. 

Beal's  Grasses  of  North  America.  For  Farmers  and  Students.  By 
Prof.  W.  J.  Beal,  of  Mich.  Agricultural  College.  Copiously 
Ill'd.     Svo.    Vol.  I.,  457  pp.    $2.50,  net.    Vol.  II.,  707  pp.     $5,  net. 

Bessey's  Botanies.     See  American  Science  Series. 

Black  and  Carter's  Natural  History  Lessons.  By  Geo.  A.  Black,  and 
Kathleen  Carter.     (For  the  very  young.)     98  pp.     50c,  net. 

Britton's  Manual  of  the  Flora  of  the  Northern  States  and  Canada.  By 
Prof.  N.  L.  Brixton,  Director  of  N.  Y.  Botanical  Garden. 

Bumpus's  Laboratory  Course  in  Invertebrate  Zoology.  By  H.  C.  Bumpus, 
Professor  in  Brown  University.      Revised.      157  pp.     $1,  net. 

Cairns's  Quantitative  Chemical  Analysis.  By  Fred'k  A.  Cairns.  Re- 
vised and  edited  by  Ur.  E.  Waller.     417  pp.     8vo.     $2,  net. 

Champlin's  Young  Folks'  Astronomy.  By  John  D.  Champlin,  Jr., 
Editor  of  Champlin's  Young  Folks'  Cyclopaedias.  Illustrated, 
vi  -f-  236  pp.     i6mo.     48c,  net. 

Congdon's  Qualitative  Analysis.  By  Ernest  A.  Congdon,  Professor 
in  Dtexel  Institute.     64  pp.      Interleaved.     Svo.     6oc,  net. 

Crozier's  Dictionary  of  Botanical  Terms.     202  pp.     Svo.     $2.40,  net. 

Hackel's  The  True  Grasses.  Translated  from  "  Die  nattirlichen 
Pflanzenfamilien "  by  F.  LAMSON-SCRIBNER  and  EFFIE  A. 
SOUTHWORTH.      V  -f-  22S  PP-      Svo.      $1.50. 

Hall's  First  Lessons  in  Experimental  Physics.  For  young  beginners, 
with  quantitative  work  for  pupils  and  lecture-table  experiments 
for  teachers.  By  Edwin  H.  Hall,  Assistant  Professor  in  Har- 
vard College,     viii  +  120  pp.     i2mo.     65c,  net. 

Hall  and  Bergen's  Text-book  of  Physics.  By  Edwin  H.  Hall,  Assist- 
ant Professor  of  Physics  in  Harvard  College,  and  Joseph  Y. 
Bergen,  Jr.,  Junior  Master  in  the  English  High  School,  Bos- 
ton.     Greatly  enlarged  edition.     596  pp.      l2mo.      $1.25,  net. 

Postage  S%  additional  on  net  books.     Descriptive  list  free. 


HENRY  HOLT  &■    CO.'S   WORKS   ON  SCIENCE. 

Hertwig's  General  Principles  of  Zoology.  From  the  Third  Edition  of 
Dr.  Richard  Hertwig's  Lehrbuch  der  Zoologie.  Translated  and 
edited  by  George  Wilton  Field,  Professor  in  Brown  Univer- 
sity.     226  pp.      8vo.     $1.60  net. 

Howell's  Dissection  of  fhe  Dog.  As  a  Basis  for  the  Study  of  Physi- 
ology. By  W.  H.  Howell,  Professor  in  the  Johns  Hopkins 
University.      100  pp.     Svo.     $1.00  net. 

Jackman"s  Nature  Study  for  the  Common  Schools.  (Arranged  by  the 
Months.)  By  WlLBUR  JACKMAN,  of  the  Cook  County  Normal 
School,  Chicago  111.     448  pp.     §1.20  net. 

Kerner  &  Oliver's  Natural  History  of  Plants.  Translated  by  Prof.  F. 
W.  Oliver,  of  University  College,  London.  4to.  4  parts. 
With  over  1000  illustrations  and  16  colored  plates.     $15.00  net. 

Kingsley's  Vertebrate  Zoology.  By  Prof.  J.  S.  Kingsley,  of  Tufts 
College.     Illustrated.     439  pp.     Svo.     $3.00  net. 

Kingsley's  Elements  of  Comparative  Zoology.    357  pp.    i2mo.    $1.20  net. 

Macalister's  Zoology  of  the  Invertebrate  and  Vertebrate  Animals.  By 
Alex.  Macalister.  Revised  by  A.  S.  Packard.  277  pp. 
l6mo.     80c.  net. 

MacDougal's  Experimental  Plant  Physiology.  On  the  Basis  of  Oels' 
Pflanzenphysiologische  Versuche.  By  D.  T.  MacDougal,  Uni- 
versity of  Minnesota,     vi  +  88  pp.     Svo.     %\.oo  net. 

Macloskie's  Elementary  Botany.  With  Students'  Guide  to  the  Exam- 
ination and  Description  of  Plants.  By  George  Macloskie, 
D.Sc,  LL.D.     373  pp.     $1.30  «rf. 

McMurrich's  Text-book  of  Invertebrate  Morphology.  By  J.  Playfair 
McMuRRICH,  M.A.,  Ph.D.,  Professor  in  the  University  of  Cin- 
cinnati,     vii  -f-  661  pp.      8vo.      New  Edition.     (3.00  net. 

McNab's  Botany.  Outlines  of  Morphology,  Physiology,  and  Classi- 
fication of  Plants.,  By  William  Ramsay  McNab.  Revised  by 
Prof.  C.  E.  Bessey.     400  pp.     i6mo.     80c.   net. 

Martin's  The  Human   Body.     See  American  Science  Series. 

*Merriam's  Mammals  of  the  Adirondack  Region,  Northeastern  New- 
York.  Willi  an  Introduction  treating  of  the  Location  and 
Boundaries  of   the  Region,  its  Geological  History,  el.  .      By  Dr. 

C.  Hart  Merriam.     316  pp.     8vo.    $3.50  net. 
Newcomb  &  Holden's  Astronomies.     See  American  Science  Series. 

Nicholson  &  Avery's  Exercises  in  Chemistry.  By  Prof.  II.  H.  Nichol- 
son, University  of  Nebraska,  and  Prof.  Samuel  Aveky,  Uni- 
versity of  Idaho.      134  pp.     60c.  net. 

*Noel's  Buz  ;  or,  The  Life  and  Adventures  of  a  Honey  Bee.  By 
Maurice  Noel.     134  pp.    $1.00. 

Noycs's  Elements  of  Qualitative  Analysis.  By  W«.  A.  Noyes,  Pro- 
fessor in  the  Rose  Polytechnic  Institute,    91  pp.    Bvo.    Soc.  net. 

Packard's  Entomology  for  Beginners.  For  the  use  <>i  Young  Folks, 
Fruit-growers,  Farmers,  and  Gardeners.     By  A.  S.   Packard. 

xvi-f-367  pp.       Third  Edition,  Revised.      $1.40  net. 
111,  1900 


HEX  AY   HOLT  cV    CO.'S    WORKS   ON  SCIENCE. 


Packard's  Guide  to  the  Study  of  Insects,  and  a  Treatise  on  those 
Injurious  and  Beneficial  to  Crops.  For  Colleges,  Farm-schools, 
and  Agriculturists.  By  A.  S.  Packard.  With  15  plates  and 
670  wood-cuts.      Ninth  Edition.      715  pp.      Svo.      $4.50  net. 

Outlines  of  Comparative  Embryology.     Illustrated.     243  pp.     8vo. 

$2.00  net. 

Zoologies.     See  American  Science  Series. 

Peabody's  Laboratory  Exercises  in  Anatomy  and    Physiology.      By  Jas. 

Edward  Peabody,  of  the   High    School    for    Boys   and    Girls, 

New    York.     x-j-79pp.      Interleaved.      l2mo.     60c.  net. 
Perkins's  Outlines  of  Electricity  and   Magnetism.      By  Prof.  Chas.  A 

PERKINS,   of    the    University   of    Tennessee.       277  pp.       121110. 

$1.10  net. 
Pierce's  Problems  in  Elementary  Physics.     Chiefly  numerical.     By  E. 

Dana  Pierce,  of  the  Hotchkiss  School.     194  pp.     60c.  net. 
*  Price's  The  Fern  Collector's  Handbook  and  Herbarium.     By  Miss  Sadie 

F.  Price.      72  plates,  mostly  life-size,  with  guide.      4to.      $2.25. 
Randolph's  Laboratory  Directions  in  General  Biology.    163  pp.    80c.  net. 
Remsen's  Chemistries.     See  American  Science  Series. 
Scudder's  Butterflies.    By  S.  H.  Scudder.    322  pp.     i2mo.    %\. 20  net. 

Brief  Guide  to  the  Commoner  Butterflies,     xi  -f  206  pp.     $1.25. 

The  same.     With  21  plates,  containing  97  illustrations.     $1.50. 

The   Life  of  a  Butterfly.     A  Chapter  in  Natural  History  for  the 

General  Reader.     By  S.  II.  Scudder.     1S6  pp.     i6mo.     80c.  net. 
Sedgwick  and  Wilson's   Biology.     See  American  Science  Series. 
*Step's  Plant  Life.    Popular  Papers.    Illustrated.    218  pp.    $100  net. 
Torrey's  Elementary   Studies  in  Chemistry.    By  Joseph   Torrey,    Jr., 

Instructor  in  Harvard.      4S7  pp.      $1.25  »et- 
Underwood's  Our  Native  Ferns  and  their  Allies.     By  Prof.  Lucien  M. 

Underwood,  of  Columbia.     156  pp.     $1.00  net. 
Underwood's  Moulds.  Mildews,  and  Mushrooms.  Ill'd.    236  pp.  $1.50  w<7. 
Williams's   Elements  of    Crystallography.     By    George    Huntington 

Williams,  late   Professor    in    the    Johns    Hopkins   University. 

x  +  270  pp.     Revised  and  Enlarged.     §1.25  net. 
Williams's    Geological    Biology.    An     Introduction   to  the  Geological 

History  of  Organisms.      By  Henry  S.  Williams,  Professor  of 

Geology  in  Yale  College.     Svo.     395  pp.     $2.80  net. 
Woodhull's  First  Course  in  Science.     By  John   F.   Woodhull,  Pro- 
fessor in  the  Teachers'  College,  New  York  City. 

I.     Book  of  Experiments,    xiv  +  79  PP-    Svo.    Paper.    50c.  net. 
II.       'Text-Took,      xv  +  133  pp.      1 21110.      Cloth.      65c.  net. 
Woodhull  and  Van   Arsdale's    Chemical  Experiments.     An    elementary 

manual,    largely  devoted    to  the    chemistry  of    every-day    life. 

Interleaved.       136  pp.      6oc.   net. 

Zimmcrmann's  Botanical  Microtechnique.  Translated  by  James  Ellis 
Humphrey,  S.C.     xii  -|  296  pp.     Svo.    $2.50  net. 

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